yep sand the neck pocket.
also, use a sanding block, not just your fingers - or you will get a wavy result - much flatter with a block.
ideally the neck should be a firm press by hand fit and you should be able to hold the neck only and have the body stay on.
if you did it so tight it was a hammer fit, you risk splitting the neck pocket - also way too tight causes too much glue to be forced out of the joint, resulting in having not enough of it holding your neck on