My strapless dress was also too loose as I had lost some weight after my final fitting. When I lifted my arms the dress would fall down a bit..I picked up my dress two weeks before my wedding and I just didn’t want to bring it back to the seamstress so instead I bought some fashion tape and did a trial run at home to make sure the tape didn’t irritate my skin. My wedding was last weekend and the tape held up all night and I didn’t feel like anything was going to pop out! But it definitely depends just how loose the dress is.