Take a shower before you leave, so the sweat is clean.
Wear different clothes for the ride.
Have a quick sponge or flannel bath in the toilets.
Backpacks can get sweaty in the heat. Many commuters use a rear rack and bag.
Consider getting a commuter bike with no suspension, slick road tyres with puncture protection, and rack eyelets. A low cost used one is fine, esp if you have a risk of theft.
Work out a plan B if you get a puncture. Do you carry a repair kit/spare tube ?

Commuting is a great way to start the day, but riding in traffic is a serious business and doing it properly will save you a lot of pain.

Read your post again and re-write, stating your question clearly in the first paragraph, and make sure you submit it by school tomorrow or you will get detention !!!!