There is a slight depression on the deck of my boat (plastic) near the front hatch (does not effect hatch). I have read about ways of repairing such things but my feeling is that since it’s not effecting performance (and most repairs involve some level of risk) and barely visible I may as well leave it as is.
My only concern is whether or not a warped deck will eventually impact the hull?
I would ignore it
A warped deck should not affect the hull. If the boat is still under warrantee, I would have a shop look at it or send a picture to the manufacturer.
Ignore it.
Ignore it
or if it bugs you maybe try to apply some heat to the area - repeated application of boiling hot wet wash cloth? Sometimes works.
Depends on what caused it
Is it a depression from resting on crossbars, or did it just appear? If the latter, it may be a thin spot in the plastic which may eventually crack.
Rotomolding is not an exact process and thin spots are more common than you might think. Manufacturers with good quality control might sell these as blems or seconds, but I’ve seen thin spots in boats being sold as first-quality.
If it is a thin spot, reinforcing it before it cracks is much easier than trying to fix a crack, and there some types of poly you can’t fix (e.g. crosslink).
G-Flex epoxy works on plastic boats; just saturate a fiberglass patch with G-flex instead of resin and apply it on the inside of the boat. Be sure and follow G-flex directions for prepping polyethylene.
You might also top-coat the patch after it cures with a layer of 3M 5200 caulk on top of the G-flex; again, prep the plastic surface around the patch carefully so the caulk will adhere better.