When you say you had fluids inside, do you mean hers? Did you ejaculate? How do you know it was her fluid? (I'm assuming that's what you mean - we filter some words here.)
If your penis was uncovered, and there was grinding with her uncovered vagina, there is a risk of HPV, herpes and syphilis. But honestly, were your pants down? I can't imagine that she'd grind on you with your pants unbuttoned and the zipper open. That would hurt her vagina.
Also, did you have underwear on? If you did, then you aren't at risk. STDs don't go through clothing.