If it is too pixelated:
1. Maybe you made it in too small of a resolution to begin with. The image is 200px wide, but you want to display it at 500px wide. You'll have to create it in the final size in the first place, preferably 2x-3x larger, then reduce to sharpen it.
2. Maybe you are viewing it at too large a magnification. It will always look worse then. View it at 1:1 to see what it really looks like on the monitor.
3. If at all possible, you should design a log in Illustrator or other vector graphics program, that way you can reduce and enlarge without loss of detail.