I'm kinda the same way. At my last competition, my coach asked me if I liked skating. I said of course. She told me to show the judges that I liked to skate. It totally changed how I skated. Suddenly, smiling didn't feel so unnatural. Often a coach will say key words that makes something click for the skater and changes their attitude.
My coach also really makes me go full out in practice. Smile, arms, down to the tiniest detail. I find that once I get over doing the arms in front of 10 skaters on the same ice that are way better and much more graceful (not that they are even watching me to begin with), it's a lot easier to do so in a competition when some kindly judges, my coach and disinterested people in the stands are watching.
I think it is just one of those things that takes time and experience to overcome. I have competed 6 times and done solos for exhibitions/shows 3 times, and I'm still really not going full out yet. Not only do I have difficulty performing, my speed and quality of skating really drops in a competition.