Hey, I am currently a high school student and will be taking the ACT for the first time in September of my 10th grade year. If I get at least a 3, (I know its unlikely on the first try) and I will probably mess up on grammar since I suck at that 
but if I do manage to get a good score do I have to take the ACT again in 11th grade?
If you get 33+, then yes.
Colleges will take a 10th grade ACT.
Colleges accept ACT tests taken during any year in high school. If you get a high score you are satisfied with, you will not have to retake unless the test you are taking in September is one without the writing section and you intend to apply to any colleges that require the writing section.
Unless your state or school district requires it, no.
Even if the state or school district requires it, you might be able to skip that test. Our state law says that all public districts are required to offer the ACT to the junior class, not that all juniors are required to take it. In fact, an ACT on a different day or the SAT would suffice. So check with your counselor on this issue if it applies to your situation. No state law should interfere with a student’s chances for a competitive college, particularly if the college or uni requires that you send ALL scores.