What a bummer! There is cold weather epoxies offored by all the manufacturers these days. However, epoxies don't just stop permanently curing because it's too cold. You could warm it up to re-start the curing. Unfortunately, now you know that temp is important and I would do a few test patches before I use the epoxy you have. I've never encountered that milky resdue you got and I've used every brand. Make sure you mix your ratios correctly and thoroughly. And give it some heat. Warm your epoxy in some warm water before using also. You could have saved the job if you warmed up the boat a few days after you discouvered it didn't cure. I'd be very suspicious of the epoxy you used.

good luck