My belly finally popped!

So this past week I've gotten a few comments about my belly. It's officially popped! But now I'm a little paranoid. I am subconciously worrying about the size of my belly. This morning my manager told me that she didn't pop until she was 5 months. I know each pregnancy is different, but I'm having trouble not comparing. My SIL is due a week before me and she was really fit before she became PG and I only imagine that now she is barely showing while I'm getting rounder by the day.

How do I get it out of my mind that it's ok to have a big baby belly, especially so early on!