The person next to me was quite large so my seat felt very small
この文章が以下のように翻訳で決ます。
隣が太った人で席が狭かった ー The person next to me was quite large so my seat felt very small
隣が ー The person next to me / the person in the seat next to me / the person next-door
太った人で ー was very large / was fat / was huge, so
席が ー my seat / the space in my seat / the space I had
狭かった ー felt very narrow / felt very small / was tiny
参考になれば嬉しいです。