I didn't say much initially. But with time to think about this, Its a good painting. Although it is not refined it captures the important structure which is the cake. Any detail beyond that is just icing. If the cake isn't there the icing doesn't do anything.
I agree with Bob73: I am usually right Like he says you might want to just start a new one and take the critique into account as far as variation in values/colors go.
If you do want to rework this one and you are worried about the painting lasting (I wouldn't be for a painting that was my first attempt) you need to follow the fat over lean rule (google it). Otherwise I would just look at it as a practice piece and worry more about trying to fix the color/values as a learning experience and don't worry about fat over lean.