miracle grow is notorious for killing little plants..
more than likely its the onset of nute burn...
miracle grow works by releasing nutes everytime you water, whether or plants need it or not... its not the best thing to start with..
you can flush the soil well with ph'd water and try to remove the nutes in it.. this should help keep your little one alive..
if it doesnt kick the bucket you should invest in some plain old potting soil without any nutrient fortification.. this will give your young plant the best chance for survival... either that, or as was said, start with jiffy pellets or rockwool cubes.. and wait until you see roots popping from them before transplantting into soil..