Some of our new grads have just taken to ER like a duck to water, others simply cannot cope with the wide range of everything you need to do, especially patients that we can't get moved out to a floor bed. They learn how to do all the immediate acute care, but have no firm grounding in the routine stuff that keeps going. I did years of medsurg, camp nursing, volunteering, and step down before coming to the ER, and still felt like a novice. It is much harder to move out of an ER to the floor, than from the floor to the ER. Since your ER doesn't allow new grads, they won't have a preceptor program in place to really teach you all the ins and outs. My ER had a 6 month program for new grads, and as I said, some fly and some wallow.
Take advantage of the floors for a while, get the time management down without the whirlwind of ED around you (not to say med-surg doesn't run at a high speed, but not quite the same broadness of diagnosis or acuity). The time spent learning to do assessments and reassessments without quite so much pressure is in my opinion very valuable.
Take the certifications available to get ready for ER ahead of time, TNCC, ACLS, ENPC.
Good luck in whatever you choose!