I get set to EN-EU all the time and not quite sure why or how to fix it. In this case it made a difference whether I put the different region in the URL though. Going to the regular link was just taking me to the Chewy page.That worked for me.
Afterwards, I had to sign out, reset myself for U.S. and log back in for regular MDE.
I booked Monday the 19th. Swolphin is completely booked those preview days.