So, we had to make character sketches for my English class (as I already said) and I want to know if anyone has any advice for me. Not grammar wise, thank you very much, but just constructive critique to help the sketch flow.

I guess I had better explain what a character sketch is, for those who don't know. It's a detailed description about a character, their physical and mental aspects. It can be a short story, but need not be.

Pacing back and forth across the wooden floor with several long strides, the petite woman looked agitated, but the expression of her actions did not reach her pale face. The soft light from the sconces on the wall showed that her face held an expression of complete composure, as if nothing could upset her, and expressed none of the worry that one would see by just watching her. Someone walked through the hall behind her and she turned her head, her black curls whipping around her face. It was just, to her dismay, one of the cleaning ladies of this house. Once the woman passed, she continued her pacing.
She stopped for a moment looked to the grand dark wooden door in front of her and glanced at the brass doorknob, as if willing it to turn would actually cause the object of her thoughts to appear. Unfortunately, she could not do magic and he did not appear. If she were able to do magic, perhaps they wouldn’t have ended up in this disaster as it was. “There’s no point in thinking about ‘if’s’, Cynthia. They do not help when there is a problem. When there is a problem, handle it. If you are unable to contain the damage it has caused, dispose of it.” Cyn’s face blanched as she thought of the words her father, a ruthless businessman, repeated to her every time during her childhood that she used the word ‘if’ when trying to solve a problem. Although she had never been eager to hear this guidance as a child, the ebony-haired women wished with every fiber in her body that her father were there now. If he were, they would not have ended up in this disaster. Thinking this only made Cyn start to pace again.
A clock chimed in the distance and the young woman continued her pacing. Every moment that passed was a moment closer to the time of her expiration. Well, perhaps that was exaggerating a bit, but not in Cyn’s mind. A moment could change everything. In a moment, one could lose their whole fortune with a gamble or investment or they could make it by winning the lottery. In Cynthia’s experience, however, it was the former that happened the most often. A roll of a die, the flipping of a card, the movements of the stock… All of those were the same to her. After all, they all played a part to land her in the position that she was currently in.
If only there were no gamblers. But then there would be investors. And if there were none of those, what else would reckless, wealthy people do with their time and money? They would dwindle and inevitably waste away out of boredom. Her thoughts had let Cynthia’s feet forget their constant tempo of back and forth, back and fourth and instead the traitorous limbs brought her to a halt in front of a mirror that hung on the wall at the opposite end of the long hall from her starting point. Although she was extremely worried, she decided that the one who she waited for would not appear at the door any quicker, whether or not she took the time to look in the mirror. What she saw did not surprise her as she looked at herself several times throughout the day, not out of vanity but out of necessity. She would not make a complete and utter spectacle of herself by looking bad even if she lost everything else. Her composure would not fail her when everything else already had.
She had appealing, albeit not stunning, facial features. She had a slightly rounded, china-doll face with small light pink lips that were almost as pale as her face itself. In truth, she was not that much paler than the next woman but her long shadowy waves and the dark clothes of mourning that she wore recently made her pallid skin stand out that much more than normal. She would have looked sickly if not for the bright green eyes that shone like emeralds cast in snow that showed her to be in good health. Her face, as usual, was about as readable as a closed book. Cynthia rarely expressed her motions with her face or her voice but instead expressed them in actions, such as pacing when she was anxious and worried.
The door opened behind her with a loud clangor as it banged against the doorstop behind it and Cyn turned around quickly. “What took you so long?” she demanded of the person who stood in the doorway.

It's good, but the only thing that I can give for advice is to ease into each new subject a little slower. That will make this flow much more smoothly & make it easier for the reader to, well, read, & understand.

All right, thanks for the advice. I'll see what I can do about that.