Slipped up is a figure of speech that means making an error or mistake. Its antonyms would be words that express the opposite of making a mistake. These could include phrases such as "nailed it," "got it right," "hit the mark," "succeeded," "accomplished," or "performed flawlessly." These words convey a sense of success and achievement, which is the opposite of slipping up. In contrast, slipping up implies falling short or failing in some way. Using antonyms of "slipped up" can convey encouragement or positivity, which could be helpful in boosting someone's morale after a mistake.