yes it's correct.
Interest is charged on credit cards just like ordinary bank accounts. So €550 @20% for one month would be €9. So €11 is probably right.
If you pay your bill in full and on time , they don't charge interest. But you didn't, so you got charged interest on the full amount, not just the balance.
AIB's rule is that you must clear two bills in full and on time to not get charged interest. So you might be charged interest next month and the following month.
If this is a once off, then you should call your credit card company and they may waive the interest.
Even better, set up a direct debit, so it doesn't happen again.
Brendan