Mirena question from new mommy

Erin • 26. Married.First baby.

So I'm getting mirena on Tuesday. had our first child back in may. We've been extra careful until this past weekend we just used the pull out method and now I'm scared to death I could be pregnant and then get the mirena and loose it or something lol!!! Which in reality I probably am not but just over reacting but still lol. They're gonna test my pee 2x but still it wouldn't show up that early also there placing it via ultrasound. Secondly once I do get mirena should we still take precaution like not let him finish inside. I don't want an ectopic pregnancy that would be horrible. I know all sounds stupid but I need advice thanks :)