Cap sleeves?

I ordered a gown with cap sleeves. (the Dynasty by Maggie Sottero). WHen I tried it on the sales person had to clip the capped sleeves because they were too big on me. I was unable to bring my arms any higher than straight out to the sides. She assured me that when I have my gown and it gets altered it will be fine and I'll be able to move my arms over my head. This is important because my FH is 6' and I'm 5'3 so I'll have to reach up to his shoulders to dance with him and stuff. I'm thinking, how is it going to be possible to move because won't the sleeves when they're sewn be the same as they were when they were clipped? I'm starting to freak out over this. My mother says that to be beautiful isnt always to be comfortable, but give me a break! I'd like to be able to dance with my new husband with out only being able to grab his waist!!

Have any of you girls worn or ordered a gown with capped sleeves and how did it turn out? Thanks!!