Hi Kiki,
In terms of fitting more of your fingers in, if you're not already using lube while you masturbate, getting some might help you feel more comfortable when inserting your fingers.
As for that feeling of needing to pee, your bladder is located right in front of the vagina (between your vagina and belly button). That means that when you do something like masturbate, which puts pressure on the front wall of the vagina and--by extension--your bladder. Our brains interpret pressure on bladder as a sign we need to pee, so that may be while you feel that way. But if you go to the bathroom before masturbating, you can feel pretty safe that you won't actually pee (if you're worried, you can even put a towel down just to be safe).
The fluid you're noticing could be a few different things. You could be ejaculating, or you could just be noticing vaginal discharge on your fingers (if it's on the thicker end, it's most likely discharge). Both of those things are normal, and you can read more about them here:
Honorably Discharged: A Guide to Vaginal Secretions,
Squirt: On Ejaculation.