There were a lot of people in line at the registers and fitting rooms, so it was annoying.
一般的に言えば、「The stores were so crowded」と「The stores were all packed」をよく使われています。
There were long lines at the registers and the fitting rooms. It was awful!
Ugh! There were tons of people in line at the register and at the fitting rooms.
「Ugh」は不満しているときに使えます。
There were line-ups at all the check-outs and fitting rooms.
All the cashiers and changing areas were super busy so it wasn't much fun.
1) There were line-ups at all the check-outs and fitting rooms.
「レジと試着室に列ができていた。」
line-up で「人の列」
check-out(s) で「レジ」
fitting room(s) で「試着室」
2) All the cashiers and changing areas were super busy so it wasn't much fun.
「レジと試着室がすごく混んでいて大変だった。」
cashier(s) で「レジ」
changing area(s) で「試着室」
ご参考になれば幸いです！
アメリカ合衆国 
日本 
