I have 4 month old baby map turtle and his shell is pretty flimsy is this normal? I'm really nervous and I don't know what else to do because he has a UVB light and a calcium block.
Not sure what you mean by flimsy... it should be slightly pliable though. Is he basking? You can skip the calcium block if it's one of those white medicated blocks as they are not proven effective.
Pick up a good pellet that has calcium in it... Baby Reptomin is a popular choice and in most pet stores. If you want to add more calcium, you can "dust" them or make your own if you use a phosphorous-free calcium supplement.
Make sure the UVB is set up correctly... it should be directly over the basking area and approximately 6-12" away.