So that $XXX potential future medical expenses fund is just a kind of escrow in case you need to draw on it for future med expenses stemming from this accident? Your back is sore, you could have done any kind of damage to it that might not show up in an x-ray. Before you settle, see a chiropractor, or better yet a DO who's also an MD. Have them check you out before you settle to make sure nothing is structurally out of whack with your spine. Explain your situation to them and ask for their advice.
Many ailments only show up years later. If this is an escrow account (they manage control of the money) or even just a promisory to pay out in the future iff you have difficulties stemming from the incident in the future, maybe you want to find out what a year's worth of regular chiropractic or osteopathic treatments will cost and give them that figure. Also get with your own insurance co. and ask them for advice--this is part of what you pay them for... There might be a legal way you can leave the amount open ended for possible future med expenses.
Plenty of people out there who settled with the best intentions, now paying for it with lingering med issues and no coverage.