Can I get some advice on ping a midterm or doing good? I feel like I'm going to fail AGAIN.?

I go to one of the best universities but it's so competitive and I have a midterm coming up for a cl that I did really bad in for the first midterm. I'm so scarrred and basically, if I don't do good, I can't go to med school (not that i know if i want to now since i did so bad before). But any help? I can't get my mind off of other things and thinking that I'm going to fail again. My friend who used to encourage me so much will not talk to me anymore because she lied about something really big and I didn't really care but she does.