Shipping doesn't switch from First Class to Priority Mail

[Food4Buns]

Hi,

trying to launch my new store and ran into a massive problem with setting up the shipping. 

Lots of my items are low in weight like only several ounces. I usually ship with USPS First Class Mail but at 16 ounces it should switch to Priority Mail because you cannot ship items over 1 lbs via First Class Mail. Problem is, it doesn't switch. It still shows the customer both options...First Class and Priority. 

Am I overlooking something?