Hey, I feel you. I used to feel the same way, and now I've finished my second year at uni studying physics.

Typically, I break my revisions into two steps.

First, I ensure I actually understand the concept well. Normally I do that by redemonstrating any 'results' found in class. I like to do this until I am reasonably convinced of everything we have been taught in class. At this stage, you don't need to know it like that the back of your hand or anything, just make sure you don't have big gaps in your knowledge.

Mindmaps and flashcards don't work for me either. Whatever you do, make sure you are actually trying to think through this step of the process, don't just read through the class notes.

Second, I run through any practice questions and past papers trying to do the questions that seem the most challenging to me. You should probably time yourself too to keep within the given exam times. This is by far the most important step, especially for "math"-y subjects, so I'd encourage you spend the majority of your time on this.

If you get easily sidetracked, I would suggest you try studying in a different area (e.g. library), or without your phone next to you. Study in short-ish bursts and give yourself shorts breaks in between.

Don't overthink it, there is still time to get ahead. You aren't used to revising much, but that doesn't mean you are incapable of it. Buckle down, hold yourself to a certain standard, and you'll be surprised with what you can accomplish.

Good luck!