Was the assignment one you were supposed to be able to work together on? If not, then by “helping”, even with 3 or 4 problems, you were technically cheating. The teacher is probably frustrated with the amount of cheating and yesterday she had had enough. That means you were the unlucky one who got singled out. You can go to the teacher privately and explain your side of it (that you didn’t understand that helping with a couple of problems would be considered cheating) and apologize and promise not to do it again. Showing that kind of maturity should make the teacher respect you more and be less likely to single you out again.