It's easy to confuse me when it comes to these cars, but I am not sure from your post whether you are having trouble getting your lid off? or putting it on securely? Both are very straightforward and easy. Taking it off requires properly loosening and gently tapping and wiggling if required until it pops loose. Then putting it on requires proper alignment (critical) and then proper tightening to a reasonable hand tight torque. There may be a torque specification but I usually just make it snug-tight checking to make sure it doesn't leak afterward. Good luck, Kurt