Endurance is what can separate a good wrestler and an awesome wrestler. Even if your opponent is stronger, faster, and more skilled, having the attitude and endurance that wrestling at the next level necessitates will allow you to beat such an opponent.
Run. Wake up in the morning before school/class/when everyone wakes up, and run a distance that makes you want to throw up. Do this at a fast pace. Do push-ups and sit-ups, as well as stretch, at both the halfway point and end point. Increase the distance of your runs every couple of days.
Eat a protein-filled breakfast.
After school, sprint repeats of 20 yards (18.3 m), no break in between, do from 15-30 depending on your fitness level. You can always do more, but make sure you sprint all the time.
Wrestle with a partner. Do the basics over and over until you can’t get them wrong. Say what you’re doing as you do the technique.
Wrestle live from anywhere from 30 minutes to an hour using round robin with at least 2 other wrestlers. Rotate opponents after each period, after each match rotates out. Always feel free to do more according to your motivation and physical condition. Also, try doing sit-ups to get those “washboard abs”.