Refusing a Paid Seat Swap

Am I the Jerk for refusing to swap seats after I paid extra? I (28 female) booked

a 6-hour flight for a work trip. I paid extra for an aisle seat near the front because

I have a bad knee and need to stretch my leg occasionally. I board early, sit down,

headphones in. A few minutes later, a woman taps me on the shoulder and asks if I can

switch seats so she can sit next to her husband. Her seat is a middle seat,

several rows back. I politely say no and explain I paid extra for this seat because of my knee.

She sighs loudly and says, “Wow… okay,” then tells her husband something under

her breath. They both start staring at me. A flight attendant comes over and asks