I can't tell you many times Barako lectured me on that.
I don't think you should showcase something that is excessively watermarked like this unless it wasn't paid for yet.
Three things I think you should keep in mind for client backgrounds: the font, the design idea, the placements and layer styles. Find a font that closely relates to the logo or just looks neutral so that it fits with the logo more. Pentool is a great way to create a great shape for your login interface as well as login buttons, although I did find it hard to work with at first you will gradually learn to use it well. The login interface is basically the face of the client background in my opinion, not the logo. It needs to stand out and compliment the logo as well as the back drop of the entire thing, using the colour schemes and creating a palette of colours will help you greatly with the addition of layer styles OR really creative uses of soft brushes.
The back drop shouldn't end up the same way you downloaded it, make a design out of it. Take different stocks, find brushes for effects you want to imitate. There's no problem with just using one image, I do it all the time but I'm trying to break out of that habit however I do make sure I do some sort of edit whether it's extremely small or to fit the overall design.
I think you can do well though, I've definitely seen people improve their designs over time here myself included but I'm still trying to improve. Looking forward to more examples