Tips on making the jv team at my high school?

I'm about 6'2 or 3 and round like 210lbs... I tried out for jv last year when I was a freshman but I went foureheeling and broke both my wrists before final cuts, i'm a sopre now and last year during tryouts I had a hard time running and no endurance, I still have that problem, I'm actually pretty good but I get kinda nervous on offense and I get tired fast and it makes my d sloppy and my offense...tge try outs are in five days and I really want to make it, so please, any thing will help...