Perhaps you could add a photo? If the oil filler cap isn't attached correctly that would account for losing a little oil, but unless you can see litres of oil all over your engine bay, there's probably another issue here as well. How many miles do you put on the car per month? The car could be burning excessive oil, which potentially indicates an issue with piston rings or other problems inside the engine. Some oil burning is to be expected, but too much indicates a bigger problem.