Should I Flush Or Just Get New Soil?

FOLKS, FOLKS, FOLKS - HERE IS MY ISSUE.
I HAVE A PLANT FROM WW SEED WHICH I PLANTED IN A SMALL POT USING SOME HYPONIX ORGANIC SOIL, RO WATER AND A 26W CFL.
EVERYTHING WAS GOING GREAT, ON ITS 3RD NODE AND HAD A REALLY NICE DARK GREEN COLOR.
I HAVE ALWAYS READ THAT THESE PLANTS LIKE ALOT OF ROOM, SO I DECIDED TO TRANSPLANT HER INTO A 4 GAL. POT WITH DRAINAGE HOLES AT THE BOTTOM.
NOW HERES WHERE I THINK MY PROBLEM STARTS. I ONLY HAD ENOUGH HYPONIX SOIL TO FILL THE POT HALFWAY SO I WENT IN MY GARAGE AND FOUN A NEW BAG OF MIRACLE GRO WHICH I MIXED WITH THE HYPONIX, THEN PLANTED AWAY.
A DAY LATER THE VERY SMALL LEAVES GROWING IN THE CENTER TURNED YELLOW AND JUST LOOK TIRED. IT HAS BEEN THIS WAY FOR ABOUT FOUR DAYS NOW AND HAS NOT BEEN GROWING AT ALL. WHAT SHOULD I DO?

get more than one cfl, and as long as the soil airy and not too dense your plant should recover

You should sit down and relax. Its going to take awhile for that plants roots to grow out to fit your 4 gallon pot. Above soil growth will slow or even seem to stop, then take off again. Widows normal finishing height is around 3', so that big of pot isn't necessary and will just prolong the grow. VV

The lower leaves will shedd as a normal part of growth. As long as its at the bottom and doesn't spread 'up' the plant its probably ok. VV

miracle grow soil has alot of nutes in it i would flush get more light and lots of air blowing on soil to dry it up.