Basic question: how to make maps appear at normal size?

Sorry, I feel like surely this has been asked before, but when I tried to use the search I got an error... So I'm trying to build a map in Roll20 for the first time.  I have a large background image which I'd like to insert before I put things on top of it.  But when I upload it to my game and drag it onto the map/background layer, it's teeny tiny.  How do I tell Roll20 to import it at 100% of its original size?   (I have not changed any settings for this map from the defaults.)

If you drag it to the map layer, it should come in at a larger size.  You can resize it by right clicking, going to advanced, and then Set Dimensions.  You can set the size in Pixels or Units (basically Roll20 grid size of 70px by 70px).