Is getting a GPA 7/10 worth asking a recommendation letter?
You might increase your chances if you find another recommender that can say better things about you. Ideally, someone with whom you already did an internship or project, who would better know how you do research. 

If you have not worked on any internship/project yet, it might still be better to ask a professor from a course in which you got a better grade. Maybe there are some basic/fundamental courses you took during your first year and whose topic is relevant for the internship.

If you still think that this professor is your best option, the argument "because most probably he will reject it" is not a reason to refrain from asking. Just go ahead and ask: the professor might agree or not, but you have nothing else to lose.