are you fundamentally evil if you need something to motivate you to do good ?

yes!
because the very idea of doing something good is that you do it because of the merit or virtue and merit of the act itself.
the moment you USE a good act to achieve some other purpose the virtuousnesses of the act is lost and the greatness of the act is gone

for eg. if u learn a concept for the higher intellectual, cognitive and aesthetic value of the concept, its why to do it.
the moment you start studying it only for the purpose of passing an upcoming exam it becomes evilish.
if you do it for the exam of life its virtuous. if you do it for what its worth to understand the basic and complex functioning of the world and help your cognitive capabilities to develop, you pay worthy respect to the REAL Meaning and purpose of the concept.

the tests for the worthiness of an act can be measured on two parameters:
THE REASON for engaging in an act.
(reason is a complex word please refer to the basic/ advanced interpretations of the word in philosophical texts.)
THE PURPOSE of the act!