First off. Never sell yourself short. You will never know what could have or should have been without applying. By the way, it seems you have the perfect undergraduate degree for your the specific Masters program you are applying to. +1
Secondly. Work through the application cycle with a sense of urgency, but do not freak out. You have more than enough time to meet the December Scholarship deadlines if you so choose, later deadlines if finances is not an issue. Just be proactive about it. It is much easier to break everything down into specific tasks, rather than chunking all together.
How about create a schedule for yourself. Within the next few days, focus on requesting Official Transcripts from your college to SOPHAS/Individual schools and reaching out to professors/bosses for letters.
By the end of the week, start your SOP. Get something down on paper, no matter how discouraging or difficult it may seem. The more time to revise, the better.
Next week, you can maybe input your credits into SOPHAS (takes 30 minutes). And begin the work experience/volunteer section. Or do whatever you would like, but it is important to start somewhere.
In terms of volunteering, never too late to start. If you are truly interested in gaining experience and fostering a relationship with a community organization or non-profit or whatever, do it. It will show that you acknowledge the need for you to expand your services. And remember, you could potentially have more than 8 months of volunteering before you enroll to apply to school if you started today!
Hang in there. Work at your own pace. But try and do a piece of the puzzle every other day at least. Good luck on the GRE if you retake and stay positive!!!!!
