DON'T use 3000x3000! That's way too big! Half that size is good to fit on most peoples' monitors without lots of off-screen stuff. You do need to increase the size on this, though. Instead of 200 pixels, which is too small, try 1500 to 2000 pixels.

You need to increase the size of your canvas on sketchbook pro. 3000x3000 pixels is a good size to start from, but obviously bigger or smaller depending on what you are drawing. The larger your canvas the more detail you can add, as with a small canvas you'll find that the image quickly becomes pixelated. You will also want to change the resolution of your image to about 300 pixels/inch, allowing for smoother lines.

The image itself has tons of potential, and you clearly have skill an artist, its just unfortunately limited by its poor resolution. I suggest looking up toonboxstudio's tutorial for solid lines on how to set up your canvas in sketchbookpro.

Also make sure you save your image as both a .tiff file and a .JPEG file separately. The JPEG file will automatically merge your layers together, whilst the .tiff file will allow you to comeback later and edit the layers. You should NOT be manually merging your layers together in the .tiff file (obviously this is not a strict rule because sometimes you should merge maybe one or two layers together, just not all of them).

You still have plenty of time, it is certainly possible for you to change the tags and use this image as a mid-development piece whilst you then boost the size of your canvas and refine it.