The term "spot-on" refers to something that is precise and accurate. Its antonyms are words that convey the opposite meaning. Words that are antonyms to spot-on include inaccurate, imprecise, mistaken, incorrect, and wrong. Inaccurate implies being incorrect, faulty or incorrect in details. Imprecise indicates a lack of exactness or detail. Mistaken suggests an error or misunderstanding. Incorrect is used when something is not accurate, right, or appropriate. Wrong means something is not right or accurate. Misguided connotes being misled or misguided. So, if something is not spot-on, it is either inaccurate, incorrect, misguided, or wrong.