The phrase "am off the mark" indicates that a statement or action is inaccurate or incorrect. Antonyms, or opposite words, for this phrase could be "on target," "accurate," or "correct." These words suggest that a statement or action is true, precise, and reliable. Other possible antonyms for "am off the mark" include "spot-on," "exact," "bang on," or "perfect." These words imply a high level of precision and confidence in the correctness of the statement or action. In contrast, antonyms for "off the mark" would be words like "wrong," "erroneous," "inaccurate," or "imprecise.