Only 3 sets of leaves does sound pretty small for week 5.
There could have been a number of facts that contributed to any issue you may be experiencing. What size area is your light in? How close do you have the light? What are the temps you are maintaining? Do you have fresh air exchange or CO2 supplementation? What kind of medium are you using? A plant can experience stunted growth from: underwatering, overwatering, overlighting, underlighting, etc. Haha, the point is that there is a "optimal" amount for all of those conditions for every plant and nearly every plant is different. Research your strain and find out what kind of conditions it thrives in and make it a point to try and recreate those conditions for your plant.
