Now I'm in a true crime movie

I'm really freaked out right now. A few minutes ago there was a knock on my door. I didn't immediately get up cause I couldn't think of anyone that would be stopping over right now. I don't have the TV or radio on so there's no noise coming from the apartment. So I start to slowly and quietly get up as the person knocks again, thinking that I'll check the peephole to see who it is, when I hear a key being put in the lock and my door being unlocked. Then I'm thinking that it's maintenance but I haven't called them. So I get to the door and undo the deadbolt and I hear the key being removed from the bottom lock. I look out the peephole and I see the back of some woman walking away with a child. I guess I scared her away when she realized somebody was home. Who the hell is she? Does she have a key to my apartment? I then heard her move to the next apartment on the other side and try that door. I don't know if she got in or what. I don't know if I should call the police or call the apartment manager but I'M REALLY FREAKED OUT. And a little scared.