@stem143 I am no expert on Miami; my son is a junior just like you, so the info I’m giving you is just from what I’ve read and/or my opinions.
You know right off the bat that a 31 on the ACT isn’t going to stand any chance of full tuition; the minimum required is 32. From reading the comments others have made, you really need a 33 or 34. Remember, though, that Miami superscores, so if you take the test several times and your highest score is 32, chances are your superscore will be one point higher.
My son has no hope of attending without a full-tuition scholarship. He has taken the ACT three times. After the second time he had a real 34 and a superscore of 35. He will take it twice in April, once for the state and once that he will pay for, in an effort to make a 36 superscore, which I think will help his chances. You might not be able to get your score that high, but I bet you can get your superscore up to 33 or 34. The more times you take it the higher the odds that you will have a high score in a single subsection, even if your composite isn’t that high. Do that enough times and you can put them together for a good superscore. So just take these tests and keep taking them.
Also, it sounds like you attend a small-town or rural high school. The redesigned SAT has less higher-level math and instead has comprehensive coverage of Algebra and Geometry, with no calculus. Since the SAT is also accepted, you might try to really bone up on the SAT math and take it a couple of times.
Good luck to you!