I would find it a bit weird if a professor in college insisted on being called by a title, correct or not, especially in the US. If you want to be called "Dr." just give a bunch of strong hints (using that title on your syllabus, and in class related communications); the savvy students will pick up quickly and the less savvy students will take leads from the more savvy ones (note: no one will use your first name if they don't know it, and even if they do, they would probably not in a professional context). Asking that the title be used explicitly just smells like insecurity, and wouldn't reflect well. Although when I was in middle school in the deep south, my teachers had to tell me to use "Sir" rather than the "Mister" I was used to (being a yankee), so what do I know.