Horrible oil leak, oil level sensor?

My oil was leaking, and my sensor was saying I had no oil even though it was full. So, I figured the oil sensor was shot.I attempted to replace it. But the replacement AutoZone gave me was too small to be the correct part. I have no idea what part it is because the one they're giving me is too small and now after replacing the oil and filter it is still pouring out from around the new part. I have no idea how to fix this because I guess I'm not correct on what piece I took out. I can't find the old piece I took out. Is there any way to help me figure this out, please? Oh, I really can't remember if the old part looked exactly like the new one or if it was bigger or just different all the way around.