So you're allowing the student to answer the questions and then go back and review them before they make a "final" answer?
You have a decision to make on how the concept of answering should work ...
Either they answer them one at a time and move on, without review, or they answer them all and are able to review them all, and then there is one button that says, "I'm done". Once they click "I'm done", the whole test is finalized.
You can't have them answer, review, answer, review, etc. You'll never know when the test is finished. There has to be some way to know when they've decided that they are satisfied with their answers.
You may want an indicator that shows which questions have not yet been answered. Perhaps they can't finalize the test until ALL questions have been answered?
.... and are the answers multiple choice, or numbers, or text? What kind of test is it?