A couple of questions:

1) is the deck / hull glassed on both sides, or only one? - humidity and temperature can have a large effect if only one side, as the wood expands and contracts with changes in both, whilst the epoxy and glass do not. - pick your moment carefully to glass the other side (when the shape is nearly the original) and then use spreader sticks until the epoxy sets.

2) when were they glassed? - epoxy takes about a week to fully harden, so if more recently, get going forcing it back into shape without delay

I did exactly the same on my first build, and forced the hull apart to match the deck, with no lasting problems (forcing it was a pain, though). It is better to force the hull than the deck, otherwise your hatches will not be the same shape as the (forced) deck.

May I also take this opportunity to welcome you to the "I will always use spreader sticks in future" club?

Cheers,

Justin