@ Dawn, now I’m going to drive you crazy with this but it seems as though you are referencing the wrong subject. In other words,
“..saw one of the hottest guys I had ever seen holding up my pen with a very amused smile.”
It sounds as though the pen is the subject of your prepositional phrase, as though it has an “amused smile”. Of course I know that’s not what you mean, but I wonder if the subject is in the wrong place with your phrase. Know what I mean?
I think that this puts your subject and prepositional phrase together:
“…saw one of the hottest guys I had ever seen, a very amused smile on his face as he held up my pen.” or make it two sentences: “…saw one of the hottest guys I had ever seen hold up my pen. There was an amused smile on his face.”
I agree smile works better than face, unless you’re saying the smile on his face as above.
Boy, do I hate line editing!