Mirena

I really like this form of birth control and my boyfriend and I always have unprotected sex and he also ejaculates inside of me. I don't mind this happening but I'm scared there might still be a decently high risk of getting pregnant. Should I stop? It says it's more than 99% effective but I'm kind of getting scared hearing people say that there's still a high chance of ectopic pregnancy. Can anyone shine some light on the situation? Thanks
Oh and I do check my vagina regularly to make sure the string is in place.