sounds to me like the RN you were working with was too caught up in trying to teach you something to care whether or not you were allowed to do a certain skill... i've learned over the last 4 years that sometimes the nurses who are most eager to teach you something are just doing so to stroke their own egos...
our school's policy is that a student cannot push a med in regular clinicals, period... same thing with starting IVs... we're taught the "theory", but not allowed to practice... but as soon as you start your final preceptorship, you're allowed to do them... it's a really big oversight when it comes to safety, IMHO, because HOW ELSE are you suppose to learn? not only that, but isn't the best time to learn such a skill is when you're being closely supervised? was the RN who was with you talk you through it?
it totally sucks that you're going to get a zero... is there any chance you can negotiate with the Instructor about your mark? ie: do an extra assignment on pushing meds or med administration safety...
do you need to pass all your clinicals in order to pass your course?
good luck with whatever happens...
beth