My biggest concern with this is, that you have again started from the small image. Since every map needs both a small & large image, it would be wisest for you to start from the large image, since it will be very difficult to create the large image from the small, but relatively simple to shrink the large to the small.
I think it would be best for you to switch to the large image now that you haven't put that much work into this image yet. It would mean redrawing your map, but trust me it's better to have to do it now rather than when you've put weeks of work in your current image.
The size difference between large & small should be at least 9% but 25% is recommended. 25% would make your large image 840 pixels wide, based on your current image.