Ahhh, I just figured it out.
I just had to delete the image I had uploaded under the "featured Image" section (Event List Settings > Media > Featured Image) and now the header is all black and looks better now.
Hi, I'm having a similar problem: my header image is all blown up and looks bad. Trying to delete/change to just plain black but can't find any help on this topic and have been searching for some time. Please help!