Can my outdoor education teacher force me to get in the pool?

"we had to get in groups and build a boat made of cardboard and then we are going to put the boat in a pool and have a race with the other groups. "

Sounds fun.

"so my group nominated me to be the one to float the boat across the pool because two of the girls are muslim and cant wear a bathing suit"

They can physically wear a bathing suit, they are simply choosing not to for religious reasons.

"and the other girl says that shes going to be on her period and cant go in the pool."

There is such thing as a tampon....

"but i really don t want to go in the pool and plus i dont even have a bathing suit because its winter rn and all my bathing suits are too small and my parents arent going to buy me another one just for this one time"

When you consider that you probably wear the new swimsuit this summer as well; your logic isn't holding up.

" i dont want to use my own money on some stupid project when i didn t even have to be the one to be in the boat. "

Understandable.

" ALSO i have the class first period and dont want to be wet the entire day"

That's a dubious claim. Bring some towels, you'll be dry in less than 30 minutes.

" AND its going to be rainy and cold outside. even though its an indoor pool,"

If it's an indoor pool, you'll be spared from the elements....

" but anyways, can the teacher force me to get in the pool? "

No, but she can fail you. Your call.

If you don' get in the pool, they should throw you in to the pool. Toughen up and do what has to be done, not what you want to do. Think of it as a job. You do realize that the reason you are paid to do a job is because it is something that you would not do otherwise. It is not fun. You are going to spend most of your adult life doing what you would rather not do, so now is the time to experience it. The better you accept it, the better the person you will be.