I have a doctors appointment at 3pm today. it is currently 8:50am. i haven't even mentioned it to my coworkers, and im having horrible anxiety about doing so. help?

So as the title says. I'm a student working in an office in between college semesters. My boss is out of the office today but I know I need to mention it to my coworkers so it doesn't look like i'm just leaving early.

Any tips or help?