'Chop my tongue off now', when you regret saying something badly and it hurt the person badly too. It's usually said directly after you've just after realising belatedly how hurtful or wrong it was.
The expression "Sorry - Chop my tongue off" is very expressive and would be understood even though it is not an English idiom.
Others that come to mind:
Kill me now.
This is more general. It is mostly said to a friend when something very embarrassing has been said or is happening. Here's how it might be used in your case.
Kill me now - I shouldn't have said that.
I should bite my tongue off, e.g.
I should bite my tongue off right now ...
The Host By Meyer, Stephenie
Note, this is not frequently used.
I think you're looking for the idiom, "to put your foot in your mouth" meaning that you've said something regrettable that hurt or embarrassed either yourself or someone else.
More information here.