Only recourse is to thoroughly wash it off immediately after spraying it, so too late now - it'll either survive or it won't, nothing you can do.

i would give it a serious watering to make the weed killer less dence . also if you water everyday it may wash the old weedkiller out . you have nothing to lose .maybe you could trickle water in constantly for a few days realy slow dripping .it mite be a bit like putting a little bit of diesal in a petrol car . what you do is either empty the tank or fill the tank right up with petrol so its just a realy weak solution of diesal. its just a thaught .