Hey, welcome to the forums.
While I am in absolutely no position to judge whether or not you're capable of catching up with the subject as I do not know where you are with your maths. I can tell you these few things.
Ive asked around and apparently alot of the basics and content from unit 1 are connected to unit 2.
Yes it is true that a lot of the content covered in unit 1 is assumed knowledge for unit 2, so it is definitely important for you to catch-up on what you missed.
The main ones you need to catch-up on are functions, this includes, being familiar with the following functions, parabolas, square root graphs, semi-circles/circles and cubics. (you'll cover more functions in unit 2 as well)
You need to be familiar with function notation and also inverse functions. You should also be able identify/determine transformations of functions.
Probability isn't really touched on that much in Unit 2, so I wouldn't make it your priority to catch up on. You should definitely have basic algebra under your belt such as factorising, solving linear/quadratics and simultaneous equations before trying to catch-up on anything.
If you're using a cambridge textbook then I would suggest this is how you plan your catch-up (I'm assuming your school covered chapters 1-9 in unit 1)
Chapter 1 and 2: (just do the chapter review to make sure you're proficient with linear stuff, if not, then go through the sub-chapters)
Chapter 3: This is entirely dependent on how comfortable you are with quadratics, a lot of it is what you may have covered in year 10 except for 3G, 3I (maybe), and 3J/K.
Chapter 4: Do everything in this chapter, I'm not saying do all questions or to spend a lot of time on it, but just make sure you are familiar with these graphs.
Chapter 5: Everything is very important in this chapter, in my opinion. (except for arrow diagrams lol)
Chapter 6: Everything except 6K
Chapter 7: 7A-7D definitely all very important, the rest are entirely dependent on your school as some schools have chosen to omit matrices as it is no longer part of the next study design.
Chapter 9: If you have time left, you may catch-up but this would be your last priority imo.
Overall, I think this is somewhat manageable to do over next few weeks + holidays.