Worried about getting pregnant

So i am 19, in college, and am absolutely terrified of getting pregnant. I'm on the pill and take it consistently (don't miss any days, but the time i take it varies 3-4 hours everyday, combination pill) and always use spermicidal condoms when i have sex. Should I actually be worried about getting pregnant? Or is it such a slim chance that I shouldn't worry? We also only have sex on my non-ovulation days, so when this app tells me chance of pregnancy is like 3%. I'm really only worried about getting pregnant because i have 18 months til i graduate college.