My shoulders got stiff because the movie I watched was so long.
The movie I watched was way too long, so my neck and shoulders got sore.
ーMy shoulders got stiff because the movie I watched was so long.
「見た映画がすごく長くて肩が凝った」
to get stiff で「肩が凝る」
ーThe movie I watched was way too long, so my neck and shoulders got sore.
「観た映画が長すぎて首と肩が痛くなった」
to get sore で「痛む」
ご参考まで！
カナダ 
