I was really acting my ass off.

我真是在演戏.
"my ass off"是固定搭配,没有实际意义,仅仅表示语气的加强
1.my ass off
to do a lot or do way too much
强调做了很多
I have been working my ass off!
2.my ass off
HAS NO MEANING,just a rhythmic expression.
无实际意义,仅用加强语气
Eminem's MY DAD'S GONE CRAZY:"I'm outta the closet,I've been lyin' my ass off".

我实在太糗了

我在出洋相
act the ass:
作糊涂事
出洋相