From high school IB I could have skipped Math 251 as well Chem 201/203 (not sure if the numbers are the same now 15 years later....). I didn't. I took the easy A's.
The GPA boost can pay off handsomely when applying for scholarships at the end of your first year and hen you are declaring your major.
First year anything isn't hard in terms of what you need to learn. It's hard because you have to adjust to all the new demands on your time. The course work takes much more time. If in science you have labs and tutorials on top of lectures. And you have to make time for drinking and partying. You'll get slammed with 5 midterms in one week etc etc.
The key to a successful first year and university career is simply organization, time management and figuring out what you can blow off and when you can blow it off. I had one semester in my third year that each of my 5 classes had labs and 3 of them also had tutorials. There were just some labs/assignments that just didn't get done to my usual standards. Don't completely skip assignments or labs..partial marks are better than no marks...but don't be afraid of not giving it your all at times. I was a TA for 4 years as I did grad school and so many of my students were just constantly stressed and they would crack. So many crying students in my office or other TAs offices over a point or two. Perhaps I was a just a dick
Take the time to slow down and enjoy life. If it means getting a poor mark on a small assignment so be it. You'll be in a much better mental state when the tests that matter come around.