I am pretty sure this is good old Poinsettia. Great when young but I've never seen OLD lush plants. Here is a link;poinsettia care
Another link to go along with my propagation comment. There is an explanation how to force your plant to color up using light/dark cycles with your grow light. How to get your poinsetta to last for months
I have to add, your plant is probably the BEST I've seen at this age indoors!!
By now you probably see that planning to purchase a new fresh plant for the holidays makes far more sense. Otherwise this plant will keep trying to find the light by lengthening its internodes and looking like a sick, vine thing. Oh it will survive but like I said I'VE never seen one of these things EVER look the way they looked fresh out of their nursery. Not even if one has a climate controlled greenhouse, great lights...they are still surviving and wimpy.