it was my bad; yeah, it was my fault
Colloquial, often used sarcastically or defiantly to admit fault in a half-hearted or exaggeratedly polite way. The form is a set phrase from 悪い + ございます (polite) in past tense.
"You were late?" "Yeah, my bad."
It was my fault, I won't do it again, so please forgive me.
From 悪い (bad) in its adverbial form 悪う + polite past ございました (from ございます). The adverbial form 悪う is a historical sound change from 悪く.