When my family and I were watching a horror movie together, my little sister screamed really loud at this one scene. and I almost froze in horror.
ーWhen my family and I were watching a horror movie together, my little sister screamed really loud at this one scene. and I almost froze in horror.
「家族と一緒にホラー映画を見ていた時、妹があるシーンで大声で叫んだので、腰を抜かしかけた」
to watch a horror movie で「ホラー映画を見る」
to scream really loud で「大声で叫ぶ」
to freeze in horror で「腰を抜かす」
ご参考まで！
カナダ 
