I feel really awkward selling ads...?

[give me love]

In my journalism class we are required to sell at least one $40 ad for our newspaper. I'm thinking about asking my orthodontist because he's very big on advertisement and stuff but I don't know how to go about doing it. I have an appointment tomorrow so should I ask then?
Should I ask him while he's there checking out my teeth or...? He's usually very busy on Saturdays so idk what he'll say or think I don't want to sound like a dumbass
Any advice?

[Creatomatic]

Ask him when he walks in the room, prior to the exam. Also might want to ask his assistant first to see how he/she suggest s asking him. Try this:
"In my journalism class we are required to sell at least one $40 ad for our newspaper. Would you be interested in purchasing add space?"