Appealing a financial aid decision

You can appeal, but realistically the appeal won't get you anything. You made more money, thus you're expected to contribute more to your own education. Appeals are effective only when some major life status not captured in the FAFSA has impacted your ability to pay for education (like birth of a special-needs child, taking over the care of an elderly parent or disabled family member, very recent job loss, major health crisis).

Hopefully, you saved some/most of that active duty pay. Make sure you're maximizing your GI bill benefits, if so eligible.