If the difference is only 2mm, then it certainly should be possible to get the two parts to match.

If you had a much bigger gap, I might suggest taking the hull and deck apart and leaving the hull in the sun all day with spreader sticks to force the hull out just slightly wider than it needs to be.

However with such a small gap, you shouldn't need to do that. Have you tried wrapping a length of rope or strap around several times and forcing wedges under the rope to increase the tension? If you put all the wedges near the edge of the deck, it should force the deck in a bit. You might need a a bit of thumping with the heel of your hand to encourage the deck to creep in.

You certainly shouldn't need to try filling the dicrepancy.