Wrong student loan repayment plan

Hey guys, this is a throwaway account because I'm just embarrassed...

I got my first job last year in January. When filling out the form for my employer when I joined, I was asked which Repayment Plan for student loans I'm on and can't remember which one I ticked, but now I think it might have been the wrong one. Stupidly of me, I only had a close look at my paycheck now to see whether the amount they are deducting is the correct one and I think I might be underpaying my loans. Now I'm scared I will get in trouble...

I'm not the strongest in maths, but as per my last payslip, I earned £2303.67 before tax, and the Student Loan deduction for it last month was £19. After looking up online, it seems like this is more in keeping with Plan 2 Repayment. However, when I applied for student loans, I was resident in Northern Ireland (Plan 1), but was going to study in England - which is why I think I got confused when ticking the right repayment plan option.

I also checked my payslips from January - August last year, (before my salary went up in September) and they seem roughly correct - I earned £2136 per month and paid off £54 in student loan deductions. So I am a little confused now.

I'm really nervous now - should I get in touch with Student Loans and explain this was an honest mistake, or... what should I do? I know I messed up.