??? :think:
I find it a bit weird that you join "Gambatte" and "Kudasai" together, as "Gambatte" is kind of exclamation-word to give encouragement, while "Kudasai" is normally use when you are making a request which is never an exclamation.
So "Gambatte" alone is sufficient, or followed by name of person or team you are rooting for, or "Gambatte, yo!" may be for informal use.