Goods bought from a shop must be fit for the purpose for which they were bought, match any description that is given and be of satisfactory quality. That means that goods should be what you reasonably expect them to be considering the price you paid. If these requirements are not met then you may have a legal right to reject them and get your money back. If you cannot get back to the shop for some days you should telephone and let the seller know that you have a problem with the goods and that you want to reject them and get a refund.
If you have kept an item for several weeks without properly checking it out and then discover a problem or fault, you may have difficulty in returning it and getting a refund because you would have had what is called ‘reasonable’ time to use the goods. There is no legal definition of what a ‘reasonable’ time is.
For more information on getting a refund when things go wrong with goods, see Common problems with products.