Very nice design! Just two points to note:
1) You'll need to avoid pure, fully saturated colors. This includes white. Aim for something closer to RGB 235/230/220 instead, and
look here for additional color recommendations.
2) Remember that flags need to be made in a 3:2 aspect ratio. When you resize this to 128 x 85 pixels, it will get stretched out and not look the way you want it. Try starting with a canvas size around 512 x 340 pixels instead.
Of course, you can make a flag that
looks like it's a different shape by using an alpha channel. Check the Tutorials sticky for more information on that. But the flag file itself needs to be in the correct proportions.
Happy drawing!
