However, in American English. Say “I feel badly” is correct and acceptable Same way I feel bad or I feel so bad is correct in British English

Hey Mari, Badly is usually correct with actions verbs rather than feelings The best way to phrase the statement is; I feel bad about what I said… Or I feel so bad about what I said .. Feel in this instance is a linking (state of being) verb rather than an action verb. That is why it does not take the adverb form. Bad is correct with feel just as it is with these linking verbs: I look bad / I looks so bad I smell bad I seem bad etc