So you are 1. Bad at tests and 2. Distracted.
Do you know why you are historically bad at tests? Is it because you are unprepared, or is there another reason such as a learning disability? If the latter is true and diagnosed, you may be able to get testing accommodations. Also, you can lay out a plan for how you intend to prepare for the classes/exams differently this time. Maybe you have a tutor, different study strategy, different materials. Maybe you plan to meet with the professor one-on-one on a set schedule. These sort of concrete changes, whether study habits or addressing a learning disability, are worth discussing.
However, if the issue of poor performance is being unprepared then you need to address what is distracting you. Have you more or less completely ceased extracurricular activities to 100% focus on studying? You should have a good explanation for why the distractions caused you to do so poorly and how ceasing them will fix it. Even with intense extracurriculars, you shouldn’t be failing a class. If the other commitments were so time consuming, that you couldn’t attend class, then I see how stopping them would lead to a better class performance. Though, I would proceed with caution if I were going to say this because not attending class may make your adviser question your commitment to school and be less willing to show you leniency.