。
I admit I was wrong.
Literal
I [subject-が] was-wrong [nominalizer-の] admit.
Casual particle drop — technically it should be 悪かったのを認めます, but the object marker を is dropped in casual speech. 悪かった literally 'was bad' = 'was wrong, was at fault.' 認める is the formal admission verb. Note the mix of casual particle-drop with the polite ~ます ending.