I think your scale is off. First, your island is 9 squares by 8 1/2 squares so 100 x 40 isn't right, it's more like 90 x 85. Second, with a mountain chain like that I'd expect something more along 900 x 900. If this were a 90 mile island then each square is 10 miles. Mountain chains are pretty wide and would probably not fit here...it would be much shorter and restricted to the main landmass chunk in the middle with maybe a low volcano on an end. I'd cut the mountains off keeping them in the middle and turn the rest into hills but I like the volcano-looking thing in the lower left and the little mountains in the east. Maybe instead of one long chain you should just do a handful of peaks and that might make the scale seem to fit better. Just whip out the eraser and erase em out a bit, pretty easy fix.
On the plus side it looks pretty good and the shape is really nice. One little fix and you're ready for towns and roads and text.