When to come to adding a logo image to your Apple Wallet design there are two options.
As default the option is set to use a square logo, the same as for the Google Wallet design. However, the Apple Wallet design will also accept a rectangle logo 480 pixels wide by 150 pixels high.
To add a rectangle logo,
Navigate to the design page
With the Apple Wallet design selected, click on the 'Theme' tab.
Scroll down the the logo image selection, and uncheck the box 'Upload a square logo'
Now upload your rectangle logo