Check the courses that you will take for all of your degree requirements. If none of them have the general chemistry course that you can skip with your AP credit as a prerequisite, then use your AP credit to fulfill the requirement. This is actually fairly likely for a mechanical engineering major.
If there are courses which do rely on the general chemistry course as a prerequisite that you need to take, then review the syllabus of the general chemistry course and try the college’s old final exams for that course. Then you can decide whether you know the material well (use your AP credit), know it well but have a few gaps (use your AP credit, but self-study the gaps), or know it poorly (consider retaking). Note that if the later course that needs general chemistry as a prerequisite is not shown in the course plan until a third semester or later, you may be able to defer the chemistry decision until after you get to campus and have a chance to talk to other students about whether the later course needs much knowledge from the general chemistry course.