Since you already made the purchase, it'll have to fit you. Fingers crossed it fits you good. keep us posted on that. Hope you can get the benefits you need from a spa.
So, very sorry what you had to go through with the back surgeries and all, it's not easy going through fusion surgery.
I have numerous back problems and declined neck surgery with all the bells and whistle of hardware this past May, one of the reasons I declined is I have rheumatoid arthritis which will deteriorate the bones further possibly making a fusion unstable, A recent bone scan showed the arthritic changes.
If you need support for your chronic pain issues then try
www.healingwell.com the chronic pain forum is good, very helpful and very supportive.
Keep us posted on how this spa works out for you.