First, can you be specific about what you don't like? Your graphic looks fine to me.
Second, when you're making an image for the screen, dpi has no meaning. (It's meaningful for print.) Your image has height and width in pixels, and it will display with that many pixels on any monitor. On screen, the image is not scaled so that each pixel is a given fraction of an inch. One pixel in an image will display as one pixel on the screen. For example, if I have a 21" monitor and a 14" monitor, both set to the same resolution, the same image will be larger on the 21", simply because the same number of pixels are spread over a larger physical area. If I have two 21" monitors, one set to 800x600 resolution and one to 1600x1200 pixel resolution, a given image will appear larger on the first monitor, because the pixels are larger. In all cases, the image is mapped pixel by pixel from the image file to the monitor. So don't worry about dpi for screen graphics.
What pixlor says is correct.
Your image seems fine. Maybe you would like to change some of the colors, to make it look better (cause not all colors look good either on screen or together with other colors), but quality is good.
Thank you all, and I'm sorry for delaying to reply earlier. Well, what I don't like about the image is that, it some how look dull to my liking. I would have wished that it will look more brighter and sharper. As hard as I have tried I haven't been able to.
I think will have to take Panos Zygopoulos advise - to work on my colors.