I'm almost 20 and my facial hair is still growing in patches. anything i can do about this?

No: Whether your beard will be thick and full or thin and patchy is about your genetics and really nothing else. I'm going to assume that your body otherwise works like a healthy young man's. Many (most?) women seem to prefer a thin-bearded, smooth man, and you're unlikely to go bald. Why not be glad for whatever Nature gave you and focus on fitness instead? That's 100% under your control.