wow , it's good question :) The meaning of "悪くない" changes depending on whether it accompanies other phrases or is used with only itself. For example , the former "私は悪くない" means It's not my fault and sounds like implying the denial of your responsibility while the latter "悪くない" means "not bad"

It looks like that you want to say " not bad" . In modern Japanese, it is まあまあです 悪 is a noun means bad thing. 悪い is an adjective means hateful; abominable; poor-looking; detestable etc.

yes, you can use it. we also often say `まあまあです` means so so.