sex advice

I recently gave birth 3 weeks ago and about a week ago I had un protected sex with my partner. It was a spur of the moment thing. And happened even though I was very worried about sex. Ino it shouldn't of happened. But it did. 😐 my boyfriend pulled out and said he didn't cum In me. But I'm still worried. I got the implant installed 5 days ago and told the nurse I didn't have sex because I felt embarrassed. Now I have no idea what to do to make sure I'm not pregnant!! Please can I have some HELPFUL advice!!