My final grade for precalc is a D+. Will this hinder my chances of getting in to George Mason University?
A D+ in precalculus suggests that you are going to have a lot of trouble if you need to take calculus in the future. Most likely you are not ready to take calculus.
You might want to do something over the summer to strengthen your math skills unless you are in a major where you do not need to take any more math.
And yes, I do understand that this does not actually answer your question.