Email template design - header image without top margin or padding

There seems to be very little control over Squarespace email template design! The header section resizes images to put extra space left and right. So I make the header empty, and use an image section as the top of my email.

I'd also like to remove the top margin/padding so my image top aligns with the top of the email. Does anyone know a way to do this? I'm looking to remove the gray space above the email content: