How harshly will a potential project supervisor judge me for doing poorly in his course? I need to choose a supervisor for my upcoming term project. I asked one of my professors if he had any ideas for a project for a student with my skill set, and he offered to supervise me as he wasn't teaching during the project timeline. 

Getting to the point, this was way early in the course, and my professor has witnessed me do terribly in the course so far. My interests lie in the subject matter of this course, and I really enjoy this prof and want to do well, but for some reason, the way we are tested really throws me off and I end up overthinking and eventually screwing up the answer. 

I'm worried about bringing the topic of my term project up to him again, because I'm worried he will not be impressed with me and refuse to work with a student doing terribly in his course. 

Should I bother talking to him about it, or should I disregard the possibility that he could be my supervisor? 

Edit: I do want to clarify that the testing style has nothing to do with what my prof asks, it is more of the type of question that throws me off... Because this is somewhat of a computer science class (which I have never taken before) we are asked to come up with algorithms on the spot, and that's what I have trouble with. I can only imagine that this can be remedied by more practice with the software we use.
When in doubt, communicate.

That is a golden rule that I have learned that works well in virtually any scenario. If you explain what you think your issues are, the prof can try to help you. Not talking to him won't magically make this go away.

If anything, he would probably think higher of you for discussing this with him.