Like others have said, the odorant settles to the bottom and gets strong when the tank runs low.  They put about a liter or so in a semi load.  Working on old LP tanks that never ran dry I have gotten that much liquid out of a 500 gallon tank.   I'm guessing you have a pilot light on something.  When it burns it really gets your attention. That is the purpose of adding it.

If you have shut off the tank you are in good shape.  Be warned, a good LP guy will do a leak test of your system before putting you back in service.  If he doesn't, consider changing companies.  That is a basic safety test you never avoid.

edit: OH! The post above about reading the tank wrong reminded me.  When you check the gauge always bang the lid against the tank a couple times.  Gauges and dials can stick and give a false reading. We used to always be able to tell when Duane had delivered to a tank with a sticky gauge.  He'd put a rock under the lid to tap on the gauge.