I am in the exact same position as you. I am taking Calc I and the average for our first midterm was 50%. I myself received a 55%. However, I talked to the professor and she told me to not worry about it. Everyone usually does poorly on the first midterm and that eventually I would realise that everything we do after this would start to become much easier. She told me to stick through it, apply myself accordingly now that I now the difficulty and do well. Easier said than done of course, but so far from assignments and what not I have been doing much better.
I am a freshman myself and while I may be wrong, I think the best advice I can give (which was initially given to me) is to stay on top of things. Read before the class starts, do all the suggested problems, use office hours and your universities math centre if you have one. All of this has so far improved my grade. As a matter of fact, I can technically still get an A in the class. 😛 Once again easier said than done, though.