The clutch has not been adjusted properly. How far is the clutch pedal above the brake pedal?
normally it should be about an inch higher than the brake pedal. To adjust it, open the bonnet and look at the gearbox, there you see the clutch cable going to the clutch lever. You can push the lever alittle towards the back of the engine bay and you will then see a small black plastic edjuster thingy, turn this so that the adjuster moves towards the back of the engine bay and closer to the lever. However it might be a case of trial and error. Preferably do this when the engine is warm. If you did it from cold it would be fine until your engine is warm, then it would do it again, since the clutch and other parts have warmed up etc.