Ehm, I know what you're talking about. I haven't really tried to fix it because honestly I wouldn't know how :/ Not without completely redrawing the bottom at least. Would you have any tips or recommendations?

Gah I'm trying to learn muscle groups but it just loosk ridiculous. Anyone willing to help? I'm really not used to shading flesh. I'm so glad I at least covered the chest. :/
By the way the problem seems a little less... prominent in the original drawing

(scanner currently out of commission so i had to use a photo)
is it just me? or should i just even out the "lump" to make it closer to a straight line than it is? (as it looks in the picture)?