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。
The person sitting beside me was really big, so I felt crowded in my seat.
この場合、次のような言い方ができますよ。
ーThe person sitting beside me was really big, so I felt crowded in my seat.
「隣に座ってた人がすごく太っていて、席がキツく感じた」
to feel crowded は狭い感じ、（スペース的に）きつい感じを表ます。
ご参考まで！
オーストラリア 
カナダ 
