My first though is it's very yellow. I think a little bit of color variation would help tremendously. If you don't want to make the ocean a blue tone, perhaps either darken the land and lighten the water a bit or vice versa? The dark brown glow around the continents might need to be a different color to compensate.

As far as the world seeming small... it's as big or as small as you want it to be. The nice thing about a map is you can put a scale on the bottom somewhere that says "1 inch is 5600 miles" and all of a sudden your planet and continents are enormous. Keep in mind that a map is supposed to convey information to its readers. If your rivers as they are now should be 12 miles wide to fit the scale... Well perhaps they are just representational of the shape and location of the rivers. If you were to stand on one of the banks perhaps it's only 1/2 a mile long. That may not show as well from as far up as we are viewing it.

If you go with the "representational" feel then the mountains may not be too large at all. The southern most mountain may indicate one huge mountain and its small surrounding peaks and range. It ends up being more stylized than exact, but that could look nice also. Some of the mountains seem to have their opacity lowered so they are slightly transparent. Intentional?

Not sure how nitpicky you want to be at this point in the development, but the continent that extends across the western edge of the map is not quite matching up on the eastern side. The northernmost edge lines up, but the others are a bit too high on the west side if my eye isn't lying to me.