It sounds a bit like you think there should be one antimatter particle for each matter particle in the universe and we don't know where all the antimatter is bu

It sounds a bit like you think there should be one antimatter particle for each matter particle in the universe and we don't know where all the antimatter is but that is not the case. There is just a lot more matter than antimatter in the (observable) universe and we have no good explanation how this came to be because there is no obvious asymmetry in the equations and one would then naturally expect equal amounts of matter and antimatter in the universe. So we don't know why we see so little antimatter, but we don't really think that it exists and is hiding somewhere, we think it never came into existence. And that is a good thing, otherwise all matter could just have turned into radiation and we couldn't exist.