。
Don't eat too much.
Literal
Too-much eat-excessively-[negative-imperative-な].
A rough negative command using the ~な prohibitive ending (distinct from the softer ~ないで). 食べ過ぎる layers the suffix 過ぎる ('to exceed') on the stem 食べ, giving 'to overeat.' Combined with あまり, the sentence literally says 'don't overeat excessively' — a mild redundancy that emphasizes the warning.