[Fishcop]

What specific primer did you use; basic acrylic or 2 part (two pack) polyurethane? If you sanded the bare metal, there's a fair chance you removed the galvanising layer, so it should be treated as a 'bare metal' restoration regardless.

You don't have to use a chromated "etch" primer, a good quality epoxy primer is arguably superior (an argument not really worth having - some prefer epoxy, some prefer etch). At the very least a good quality 'direct to metal' (DTM) primer/filler should have been used.

Find a sacrificial area and "poke it with a stick" and see if you can get it to lift... if not, don't stress, you're probably fine. If it does lift, it's best you know now and can repair/redo as necessary...