Changing the resolution doesn't help. It's running Windows 7, it's been like this since I bought it. It doesn't affect my use of the computer at all (it runs fine), it's just irritating that everything in programs is smaller (not games for some reason though).
Plugging it into the TV via HDMI makes everything 'normal' (as in the same as other computers) resolution. I've tried changing the screen resolution, which does make everything larger, but it doesn't take up the whole screen, is this because of the laptop monitor or something?

Not to be Admiral Obvious here, but did you check if the display of your laptops monitor is set right?