Yes, epoxy do shrink. Most epoxies just 2% or so, but cheaper ones can shrink more. If the mix ratio is not correct shrinking can increase. Another increasing thing is if you have any solvents mixed in epoxy.

: Does epoxy shrink when it dries?? I coated the underside of my deck
: yesterday. Put it on this morning and it has drawn up big time. It's going
: to take some serious force to pull it back into shape. I expected some
: movement but nothing like this!