I just don't think it is a needle issue but I could be wrong. I do know there is a top and bottom to W&N here is what their web site says
Is there a top and bottom side to Warm & Natural?
Yes. The side with "flecks" (plant and leaf particles) is the top side. The whiter side is the bottom side. If you iron a quilt or wearable made with Warm & Natural, press with the top side toward the iron and make sure your iron is on a low setting. If you make a white quilt consider quilting with Warm & Natural bottom side up.
So based on this answer this is not what is causing your problem. Broadcloth usually has a fairly tight weave to it, is that how your back looks? Is it pretty tightly woven? Maybe your needle is dull or one of the needles in the pack is defective. Try pulling a different needle out of the package and see if that helps alliviate the problem.