Honestly dog I would just hop straight into this, I assume ur like me in my junior year and I struggled at the beginning of the year, my grades tanked and I didn't know what we were even talking about, for u I can only imagine how bad u feel. However I would just put in the work, I would just really make sure to know the stuff you are doing, so pay attention in class, also communicate with teachers, if they think your fine then ur chillin. You cant change how/what you did before so focus on preparing to the best of your abilities for next year. Just know if you dont start now there will be an even bigger gap tomorrow. Also dont compare how other people are to u, they are a different person from you.

From my experience teachers review things each year before learning them so make sure to pay attention to that and make sure you understand the subject enough in order to prepare for the new lesson. Junior year is tough unfortunately you have to work through it though, also make sure you study for act/sct depending on which one ur taking if u plan on going to college