the truth is, your growing great genetic in a very weak manner... until the sun come out for long AND it warms up above 70* and u can put it outside u need to get a few mini flouros from home depot and keep them on 18/6 unitl its warm enough
forget trying to catch wat little sunlight there is........ what latitude are u on, like, north us, central us, south us... or get a nice high intensity discharge lamp, aka HID lamps, they come in a few kinds, most common 400-1000watt metal halide, or MH... and HPS, high pressure sodium lamps... MH is good for veg, HPS is for flower but can be used for veg.. uses a lot of energy too...
but cheep way is to use miniflouros from home depot, get like 2 100w 6500k (kelvin) and keep them an inch or 2 above them