I would not avoid feeding for a few weeks. Offer him a meal the size you normally would next week. If he refuses dont worry about it, but if he takes it thats fine too. Its ok for them to have a bit bigger meal one week. Im sure sometime in the future the petstore may be outta the normal sized meals so you have to give him a bit smaller meal that week. Itll be fine either way, i just wouldnt make a habit out of either.