Mine took a while, but it got increasingly shallow and is finally flat with the top edge protruding a bit. (I'm 40 weeks today - I think that this one might go a little over...!)

It's nowhere near as 'outie' as some women get. I wonder if it is because my bub is posterior (back against right side), which usually means that the front of the belly stays a little flatter than when they are anterior?

Not that it's the end of the world, but I hope that mine goes back properly, I had such a cute little belly button... (LOL)!!