If you are not satisfied with your standardized test scores, it is not too late to take action. Perhaps your overall score is lower than you expected or there are areas that you thought you should have performed better than the numbers show. Here's the good news, there is always a course of action.
Be aware that college admissions boards consider tests scores as one of the factors of college admittance, but it is not the only one. If your application profile includes a rigorous course load, a GPA that you are proud of, and some extra-curricular activities or community experiences that have taught you significant life lessons or made you an interesting and mature young adult, than you are on the right track. However, the test scores are still significant and if you feel low test scores might hold you back from acceptance at some schools, you need to ask yourself a few questions.
First, consider if you are taking the correct test for you. Colleges don't prefer one over the other, but there are differences. ACT contains a section on science and the SAT does not. The SAT has an additional reading passage, but also a little more time allowed. It is important to understand the differences between the two tests and see if taking a different test would glean a better score. Find out the test timelines, make your decision and re-test.
Second, consider if you have sufficiently prepared for the test. Testing is like racing; you only get good at it if you do it. Most people can't race once and win the blue ribbon. Do you have the time and fortitude to study 2-3 hours each week or even 4-6 hours each month? If so, are you willing to commit to the task? Realistically, some settle for the lower test score and some commit to the time. Studying and test prep is one of those situations where you really get out of it what you put into it. If you commit to a good test prep course, whether is be a self-study in a book or online, or you take a class, the pay-off is real in terms of raising your test score 1-4 points or more on the ACT and your SAT by 100-160 points or more.
Finally, be aware of test optional colleges. There are some students who experience test anxiety or may struggle with the idea of high stakes testing. If you have attempted preparation for testing and failed, or have worked with professionals on managing stress related to testing, or have other concerns related to testing, perhaps you should consider test optional schools. There are over 800 major colleges and universities (about 1/3 of all US colleges) now have test-optional admissions opportunities.
If you have figured out that you are taking the test that best shows your strengths, and you put quality time into studying and being prepared for the test, then you can confidently say you have done what you can to prepare for your standardized test experience.