And I didn't even need to sew it on, I just pinned it from the inside using tiny safety pins. I added several extra strips of rhinestones to make it fit closer (so it's not too big) and cover me up a bit more. I even had enough left over to make a matching rhinestone choker:
Depending on how demure I want to be, I can add more and more rhinestone strips to close it up even more along the split up the leg. This will come in handy if I actually want to dance in the dress. So I get an A+ for resourcefulness. From too big and showing too much skin to fitting and more demure in just 5 minutes.
Original dress (before):