We say "it backfired"

thank you - but are there any other idioms??

how about "it (a plan, good intention, etc) blew up in my face" or "it went awry"?

Those both meant approximately the same things as "backfiring"

Schemann/Knight, German-English Dictionary of Idioms:
etw. ist ein Schuß nach hinten / ein Schuß geht nach hinten los ugs.
s.th. backfires, + s.o. scores an own goal

"s.th. backfires" is the closest equivalent to "der Schuß geht nach hinten los" (an action has unintended negative consequences). "to score an own goal" --> "ein Eigentor schiessen" may also work.

The meaning of "schlafende Hunde wecken" is different and the related English saying is "Let sleeping dogs lie" (don't rekindle an old conflict, don't rehash an old problem).

Schemann/Knight, German-English Dictionary of Idioms:
etw. ist ein Schuß nach hinten / ein Schuß geht nach hinten los ugs.
s.th. backfires, + s.o. scores an own goal

"s.th. backfires" is the closest equivalent to "der Schuß geht nach hinten los" (an action has unintended negative consequences). "to score an own goal" --> "ein Eigentor schiessen" may also work.

The meaning of "schlafende Hunde wecken" is different and the related English saying is "Let sleeping dogs lie" (don't rekindle an old conflict, don't rehash an old problem).

Schemann/Knight, German-English Dictionary of Idioms:
etw. ist ein Schuß nach hinten / ein Schuß geht nach hinten los ugs.
s.th. backfires, + s.o. scores an own goal

"s.th. backfires" is the closest equivalent to "der Schuß geht nach hinten los" (an action has unintended negative consequences). "to score an own goal" --> "ein Eigentor schiessen" may also work.

The meaning of "schlafende Hunde wecken" is different and the related English saying is "Let sleeping dogs lie" (don't rekindle an old conflict, don't rehash an old problem).

Sorry for posting in triplicate. The submission seemed to be hanging so I impatiently clicked the send button again (twice).