okay so today i went and put on some acrylic urethane varnish i was wondering will it peel off in the water or is it water proof? really hoping its water proof if not idk lol. has anyone ever used it?
so its waterproof and wont come off one day?
What type of resin did you use?
regular polyester resin 
You should be good then. acrylics are solid sealers for polyester, but I heard not to use them epoxy. I don't deal with epoxy though so its okay
It should last. I haven't used acrylic urethane, but I've heard of people that have, and I think that they like it. I know minwax makes some.
I am assuming that you are finishing with a sanded hotcoat, so sand it to 320 or so and wipe 2-3 coats on each side. a sealer really serves no structural purpose though. You should not be using it to cover up sandthroughs and what not. but to answer your question, it'll last as long as any other high performance shortboard with a sanded only finsh does, so make sure you do agood hot coat and sand well and you should be fine with using it as a sealer