lol I feel like a moron, I'm so sorry!Make sure you have a layer mask added to whichever layer is taking up most space on the banner, in order to blend. Also make sure the layer mask is selected when you are using your brush. Layer mask should be white, and your brush should be black. Does that make sense?
I don't know if I have black selected is that the black square at the bottom of the tool area? Do my settings look right? I have the layer mask... I think.