You're EXTREMELY close. The most notable thing is that the sourced belly is of a lot different quality than your model. Matching the skintones isn't too hard, but when the two are that dissimilar, it's hard to sell the match.
In conclusion, two friendly suggestions:
Dig through a gallery featuring hi-quality pregnant ladies and find one posing in a similar pose. (I hate it when they wrap their arms around the belly, makes it impossible to use; but sorry, digressing.) Also remember that it's easier to degrade an image to match than it is to try and make something shot with a phone camera look like studio photography.
And Secondly, apply a Curves Adjustment Layer to just the belly layer. (If you Alt-click between them, your cursor becomes an arrow that will make the Curves into a slave, which means you can color-match to your heart's content without doing any permanent changes) With the curve, change the top setting from RGB to just Red, if the belly needs more red, or just Blue if the belly is too warm or too cool. By pulling the Blue curve downward, you introduce more yellow, which tends to be what 99% of the bellies I've shopped have needed.
This was super verbose. If I've talked over you too much, please message me, I can break it down better.