Let's fill in the gaps with the correct form of the words.
- The word in the first gap is much. We need a comparative form because of "not", so the correct form is much fun.
- The word in the second gap is little. We need a comparative form as the sentence continues with "than", so the correct form is less.
So, the text will be:
Cody was very sad. "OK, it will be zero fun, not much gym and the Project will be less interesting than science, I am sure!