Longhorn,
You do not need to sandblast again and redo it. All you need to do it take the sheen off the coat with some 600 grit sand paper, then marine clean, metal ready and reapply. It will be as good as new.
You brushed it on right? You never thinned out the POR15 did you? It seems as though it just did not cover well.
You would know if it did not stick to the metal as it peels off like duct tape, it big pieces. I do not think it had an issue sticking with the metal, it just seems like it did not cover well.
When I did mine I used metal ready and left it for a day and it rusted all to heck. I just went ahead and put the por15 over the rust and it worked excellent!
