Having issues holding temp

I am having a lot of trouble getting my building to temp and keeping it there. My chicks will be arriving within the next few days and I am afraid I will chill them. I have 150 arriving this week and then a sportsman hatching on Monday. So I really need advise on fixing this issue. I have one pen that is spprox 4'x16 and the other is approx 8'x16 and neither is staying warm. The smaller pen has 2 heat lamps in it and the larger has a large heat lamp that uses 3 bulbs and has about a 3-4' shield

I wouldnt worry about the entire building temp, what is the floor temp near the bulbs?
Is the building insulated and draft free?

It isnot insulated, but is draft free. I have not measured the temp right under the heat lamp will do that today. I am also thinking I may place the chicks and turkeys into the turkey pen together for a few weeks and then seperate them once they feather out. That way they will all be in a smaller area which will be easier to keep warm. I am also going to move the big heat lamp into that area. Fingers crossed and prayers going that they will be warm enough. I am also going to put a small heater into the coop to help with the temp

If it is not insulated then yes you are going to have some heat loss. But I would put a few different heat lamps so they do not all huddle under one.