sounds like you were looking to enter the shallows and accidentally got yourself stuck in deep ocean.
Yeah, you can exit. Look at the chunk map and find the room #1, or at least head 'downward' in room numbers. Eventually you'll hit the edge and get back in your boat.
Keep your platforms handy and try to just super-jump/stormdash your way out of there. Or, well, have some fun exploring the oceans.
Not much in there currently though.