There isn't a turtle called a Yellow Belly Map. There are Yellow Belly Sliders (Trachemys scripta scripta) and Yellow-Blotched Maps (Graptemys flavimaculata. People are always calling turtles by the wrong name. It makes it very hard to learn how to care for the turtle properly. You should always ask the seller to provide the scientific name when purchasing turtles. If they can not provide it, move on.
Providing good, clear pics of the turtle, describing the habitat, water and basking temps, foods offered and how much, how often etc. we can ID the turtle for you and give you some ideas. Ideally though, slow and steady growth is what you are after.
Sep 06, 2009
Yellow Bellied Map Turtle by: Shelly
Is it possible your yellow bellied map turtle is full grown?
Here is a place for some specific information for you.