to answer your first question about the bleeding, no you didn't puncture anything or hit anything if you pulled up a flap of skin and inserted the needle there. Sometimes when they move alot they will bleed when you pull the needle out, or sometimes they'll just bleed no matter what. you didn't hurt him so don't worry. the poke of the needle is more of a shock and it feels strange to them to have something sitting in their skin pushing fluid into them.
I assume your giving Norm-R or lactaided ringers right? I'd give the 100ccs for the rest of the prescribed time. YOu do not want to stop every time he has solid stools because then you'll just be circling around with soft and hard stools.
oh and to see if he's really dehydrated, if you pull up on the skin and it stays there or receeds really really slowly then he's dehydrated. if the skin bounces back quickly then he should be ok. HOWEVER that's not always a sure fire way to tell.
Lastly, you shouldn't use hte same exact spot every time. If your doing the fluids in the back of the neck then you can do left side, middle, and right side. Basically you can stick the fluids anywhere there is enough of a flap of skin to stick the needle in without hitting muscle.
hope this helps you out
good luck