If you want to increase your yield, go to 18/6 ASAP, your autos won't yield or grow as much at just 12/12.
Stretching your plants won't work either, there will just be bigger gaps between the nodes. The flowers will only grow as big as they are genetically programmed to, there is no way to cause extra large growth. All you can do is to provide optimal conditions which will allow your plant to then grow her optimal flowers.
Also, forget the molasses, it is BS, give your plants fulvic acid, humic acid or amino acids (or all 3 for best results!), and this will do 10,000 times more benefit for your plant than any sugar water ever will.
Hope this helps,............
Organoman.