In your case, with the gun on your back seat covered up instead of concealed in a holster on your body I think you did the right thing.

With that said what the heck does a car lot have to do with carrying concealed?

I don't know about Indiana but Florida does not require you to inform the officer. If I am carrying, I always am, I do not volunteer the information of that fact unless they ask. If they see my CWP and ask if I am carrying then I will tell them "of course".