hey first of all, please don't feel discouraged because perms and combs are difficult for most people in fact its the most aids topic in 3u imo. if your school is starting off y11 with perms and combs you probably also go to a relatively highly ranked school and the content you covered is probably hard. some selective schools often do this so that they can be efficient and not have overlap with the 2u and 3u functions topic, or to prime kids to do 4u by pushing them hard. an older cousin told me her school did it so it could prompt a kids that didn't do well to drop out of 3u to ensure that those who did okay ish will get the school better results, not sure how true that is but anyways you shouldn't take the bait. for reference a lot of schools started off with functions and trig for 3u or some shit like that, which is considerably easier (depends on the person but yk). most schools do combs for the prelim yearly exam.
also y11 doesn't count towards hsc, just early entry if you want it ig, so i would advice you to take it out of your head that this mark might affect how you'll do in your hsc. if anything this is your sign to have your academic comeback for y12 lol
im currently accelerating and in my hsc year for 2u, so i think i'm inclined to say that you should keep 3u. it seems like you actually like math, and in my opinion 2u is not too hard, especially considering that the hardest it gets in hsc 2u is far from what combs are like (for me at least). combs are one of the hardest concepts covered in the prelim 3u course, so i think you should hang on and see how you go for this coming term and make your decision based off that. if you still find it really hard after that i would suggest you drop it.
perms and combs really requires a conceptual understanding of what is happening and lots of practice with a wide variety of problems. i mean HEAPS of practice. i think you should work with your teacher and see if they are willing to help you better understand things or if they can provide you resources like practice questions and things like that. tutoring helped me, but it's crazy expensive and I think it important you have someone to fully explain things to you so you understand, but that's totally up to you. also if you're unaware there is this site called thsc (
https://thsconline.github.io/s/) which gives you access to years of past papers for math from a range of schools, so going through those might help too.
just to end it off id like to remind you that most people hate combs and a lot more ppl that you think go into 12 still flopping combs so don't be sad you're not doing great in term 1 of y11. you still have an opportunity to grow from this task and do better if you choose to put in the work. good luck!