They're not Economy Plus, whether they have a little more legroom than regular economy I don't know but you can clearly see on Aerolopa (https://www.aerolopa.com/ua-boeing-78p) that the D-F and J-L sections have the same number of seats squeezed into a smaller space than the A-C section. I would not expect to get a refund based on claimed confusion or mislabeling. You'd be getting what UA considers a "Preferred" seat for your $77 regardless.