First things first. Deep breaths. Give yourself a minute. It's okay.
You have a few options. To help yourself understand the maths, you could use Khan Academy and similar websites. You can start from whatever point you need and work through everything at your own pace until you understand it. It's really helpful for filling gaps in your knowledge that could be making things difficult.
You can also talk to your teacher. They might be able to help you through the things you're struggling with, either in class, at lunch breaks or after school. This way you get one on one support that could really help.
Another option is to see if you can change subjects or go down a level. Your school might let you take something like Biology, Chemistry or Computing instead of Mathematics if you feel like you'd do better with those. They might also let you take Intermediate 2 (Int 2) instead of Higher, especially if you're in 5th year and planning to go onto 6th year (so you could do Higher in 6th). You might find the int 2 work much easier to cope with and be able to improve your skills through it, and then cope better with Higher next year.
Depending on what you're wanting to study at university, having maths may or may not be important. Mathematics, Computer Science, Physics and Engineering pretty much all have it as a hard requirement; most science subjects will accept it, but will also happily take things like Biology and Chemistry; humanities and social sciences generally just treat it as another grade. What is it you're wanting to study at university?
There are always alternatives to university, as well. You can get an apprenticeship, go to college, or if you want a degree there's always The Open University. They don't have entry requirements and they have pretty much every general science available as a subject, although you're not going to find anything specific like zoology - it'd just be in biology and environmental science. You could also look into other universities and see if their entry requirements are manageable, or look into studying a different subject that doesn't require sciences. It isn't the end of the world to not get into the university you're thinking about right now.
Failing all that, it might be entirely normal to find the course hard at this point. It's worth checking with your classmates.
Good luck.