Without pictures it is hard to say what you are seeing. But from my experience, the plant is just starting to hit vegetative stride at the third set of leaves. It shouldn't be pre-flowering yet.

From what I've seen & read, pre-flowering doesn't happen until somewhere around the 4th week of vegetative growth. Vegetative growth doesn't begin until 2 or so weeks after sprouting.

To quote from "Marijuana Horticulture The Indoor/Outdoor Medical Grower's Bible, 5th Ed." from Jorge Cedrvantes, page 75:
"The pre-flowers grow at branch internodes just behind the leaf spur or stipule about the forth week of vegetative growth, when the plant is six to eight weeks old."

I've had plants show preflowers at 4-5 weeks from sprouting, but not at 2.

Grow