Ah yes, the seatings. Lyndsey, I can honestly tell you that with one exception we have had great tablemates on all of our cruises, which goes back to 1992. We have enjoyed some more than others, but generally everyone has gotten along well. We have had two memorable cruises just because of the tablemates. In the first case, it was two couples from Canada who were much older than us but we struck it off well and looked forward to seeing each other every day. They were wonderful! They were of Italian heritage and one night the two husbands serenaded the dining room with O Solo Mio. They got a standing ovation and our table got two bottles of wine! The most recent example was on the Carnival Legend last year, where we had a couple our age - along with their son who was close to our son's age. We all became great cruise buddies.
So - don't fret! In most cases it will work out. If it doesn't, just do as Nancy says and speak to the dining room management. They'll take care of it.