There's no limit to how many times you can take the ACT. Does it look bad if you take it many times? No, but I would advise taking the test for the sake of taking it. I do suggest that prior to each exam, you complete at least 6 full length practice tests. At this point you're going to be as ready as possible to take the ACT.
Once you reach the score you need, it's advisable that you stop preparing for the exam and begin working on other aspects of your college application including exploring areas of personal interest, hobbies, etc. For example, let's say you really want to attend University ABC and you learn that the average ACT score they accept is between a 28 and 32. If on your first attempt you score a 32, please stop testing - congratulations, you hit your goal it's time to move on.
What I find is that you should stop taking the ACT when your score stops moving; you should probably know after 3 ACT tests are taken.