I can't stop worrying about cross country tomorrow and I'm crying?

I'm 14 and I came 19th of about 60 in cross country for PE , now I have to do it tomorrow. I'm year nine but tmorrow it's year seven, eight, nine, ten and eleven. I've been overweight in the last but I lost lots of weight, I know I'm not overweight but my closest friends who are doing it are underweight , I'm not exaggerating they are. Anyway , I'm curvy sure but not fat. I'm just scared because boys are doing too including a really cute sporty guy I had an enormous crush on in the past. I'm gonna be hot, sweaty and if I do well I have to go to another competition but if I do bad I look like an unfit freak. I guess something I'm really scared of is being the fat girl again and that's how I feel, Ido paranoid that I'm her and that's how people see me. I was just crying t my mum but she said she didn't get hy I was so upset and blah blah blah but I am and I have to do it. Please help, I need reassurance