According to the website I own 1803 games but Galaxy says I only own 1792. I know the Warsaw Rising game that was recently released for free is among the missing but beyond that I have no idea what the others might be. Is there someway GOG can check and fix the issue?

Unlike the website, GOG Galaxy doesn't list most non-games, like The Witcher Goodies Collection for example. It's unlikely they'll address this in the foreseeable future.

If actual games are missing, you'll have to open a support ticket.

I might be wrong, but games that has two versions that are merged into one item in Galaxy propably only counts as one.