Increase the height or decrease the width. Instead of 400 by 100 try 400 by 150 or higher. But not bad for beginner. Try some Tutorials by searching through google, take your time, and don't rush, I take my time with my works and I like the results. If you take your time and you like your results, then that is an improvement. But try tutorials or developing your own style of choice by practicing and not being afraid to use simple brushes or C4D's or smudging techniques, anythign to help figure out what you like most.
I was also like you, a beginner in PS and now that I took some tutorials and practiced, I've gotten better at my works. So just practice and you'll be a great GFXer.