If you have physically met face to face at any point, or if it is with a shop which doesn’t make a habit of selling in this way, you won’t be covered and should look to Sale of Goods legislation instead.
you will be fine. my mate bought a very expensive monitor from ocuk (over £300) and when he got home he realised he didnt have the correct output from his gpu to his nice new monitor. went back to ocuk next day and told them that he hadnt done his homework properly and they allowed him to have a refund and he then purchased a different monitor.