-chuckles- Let me find another sample. Not sure what your learning style is but I found glancing at other people's work to help me when I'm stuck on certain areas.
Also, if in doubt, ask another artist to look at the art. I use to bug my friend on another site with each piece and she was like, your getting good after pointing out things I needed to fix or not sure if there is thread like this but me and another group of people use to have a thread called 'Red Lines'. Basically people would post WIPs and someone would take the piece and using the red pencil on their choice of programs, hence the name red lines, they would mark suggestions on the WIP for the artist to fix certain areas. The artist didn't have to go with the suggestions, merely it was to show what could be improved and all.
and on that note, I found these so I'll use them as my samples.. since I can't go back and edit them no more, I can be like.. o 0 my style was crud back than and feel totally fine about it..
The actual WIP.. I usually never keep WIPs but in case, kind of glad I did.. and glancing at it, the chest without any shading details does look bigger than I intended it to be.. This was one of the small sketches I had done of my OC, Chloe back when I wasn't sure what the hell the poor girl looked like... and there is no way she has a big chest..
The end result.. after adding in the shading and other small details, also remember.. unless your drawing the character naked.. how the clothes lay around the chest could also make the chest appear bigger than the actual size cause unless the girl is wearing tight ass clothes that are hugging her boobies like pythons..
Hope that helps a little bit. And as promised:
^ ^ This tutorial shows some more boobie samples but cause it's basically about how to draw females, might aid you more.