You can't take something back to the shop and expect to get a refund or exchange just because "it looked much better on the model".The item has to be faulty or not fit for purpose to have any legal right to refund.The shop may take the item back as a courtesy but they are under no legal obligation to do so.
Sorry, but you can't really exchange or get refunds for sale items unless they were faulty.
But if the item looked better on the model wearing it, perhaps you could offer it to a friend?