Low Oil LIght question??

Ok everytime i park my car on a hill where the front of the car is facing down, the low oil light comes on. Today i checked the level of the oil, and it was below the half way mark, it was towrds the min side. I wont be able to get my oil changed till saturday, mean while i have school and some times when i am about to come home i get the low oil light, i dont want drive my car when the light is on.I would change the oil my self but i dont have some of the tools to do it. So should i just add some oil, and if so is castrol 10w-40 ok. Would this casue any problems, because ford uses a different oil than the one that i am about to use.

Thanks

anyone??

Thanks

I think i am about to go do that right now

I had it parked on an even surface when i checked the level, it was below the half way mark.