1. If I just leave it alone will it cause a problem? NO.
2. Is there an easy fix, like pigtail with a wire nut to make one connection? YES, NO.
3. If not able to fix it correctly with a pigtail what is the correct way to fix it, and can it be done DIY. ADD BUSS BAR EXTENSION
4. I am not sure but is it ok to doubling up on the ground bar? NO