Question

If you haven't done Maths C in High School is it difficult to do Maths in University

Answer 1

What is "Maths C"?
University level math often begins with Pre-Calculus. However, some more prestigious schools, expect you to already have taken pre-calculus in high school and start with Calculus as first year mathematics. So you need to look that up at your school.
But, you should feel comfortable with your basic algebra and trigonometry by the time you reach university level mathematics Because by the time you reach a Uni, lectures go much faster than they did in HS, which is where most students struggle.

1 lecture in Uni = 2-3 sections in a math chapter.