This is a manifestation of obsessive-compulsive disorder, and I am always not sure what I am doing.

There are two solutions:

Force yourself not to check first, and then check after all the questions are finished.

Second, usually do more problems, enrich the thinking of solving problems, and improve the ability and accuracy of solving problems. In this way, even if you do a problem, you can finish it quickly and there will be no shortage of time.