There are different schools of thought on whether it serves to second guess multiple choice answers on standardized tests. Each of us has our own rhythm, our own approach, and our own insecurities when it comes to taking these tests; when the gentle balance of this equilibrium is interrupted by a hard question, we can easily find ourselves on the road of self-doubt. Every question thereafter can become a new battle of confidence. We look for reasons why any of the answers might be right, and why our answer might be wrong.
In such moments, take a deep breath, take your eyes off the page, refocus, and remember that in the ACT and SAT, there is de facto only ever one right answer to each question. Once you've found it, you can move on. In this game, confidence is the key to success, and we should not be our own worst enemies in this experience. Each question is its own piece of real estate, so whatever happened on the questions prior, the next one is new and you can trust yourself to tackle it.
When I was taking the standardized tests for college, I read an article stating that women spend more time going back and second guessing than men do, and are more likely to be affected by performance-inhibiting self-doubt in the test environment. Since that moment I made it a point to notice when I was engaging in this behavior negatively, and give myself a shot at shaking it off. I encourage all students to do the same. Be thoughtful, be confident, and you'll own it.