Proving a transaction is mine
See Is there a way to prove ownership of a transaction?, which suggests using the private key to sign a message. You could send a signed message to your professor with the transaction id. However, since you say you're in different groups, it can still be that someone from another group just uses your transaction id, and doesn't get caught.

I would suggest asking your professor to give everyone a different wallet address to transfer the money to, or to request that everyone signs his transaction id with the private key used for the transaction.