oh Bizi.
at least, we DO have make-up. so try not to add the embarrassment about looks to the existing anxiety. you can make your face look "normal" for the inservice and it will only be for half an hour, plus maybe an extra quarter hour or so if there are questions or you are asked for business cards, etc.
Speaking of which... DO remember to bring a stack of business cards. Come to think of it, i would not wait for requests but hand them out matter-of-factedly to all the staff members present, at the end of your presentation, when you are at the "you can give them my number" stage.
Anyway. About your looks. Remember you have a beautiful inner glow and that will radiate through.

You also have a lovely smile which will decorate your face even better than the makeup.
love
~ waves ~