One member here puts a thin layer of plastic over his seeded area (much smaller area no doubt) ...and then lets the sun heat it up like a terrarium. he would lift up the plastic to water and put it back in place after watering. he had great success with this method. Pics of his yard looked great. Maybe he'll chime in here if he see's this post.
Hey, I think that's me.
You said plastic netting. Is it netting or a plastic sheet?
Yes, any clumps of hay/straw will cause issues. When you spread it around, in general, you should be able to almost see through the hay to the ground. The purpose is just to hold moisture.
How long was the cover (hay and plastic) on the new seed? Depending on climate, I pull the plastic after no longer then 2 weeks. At that point, I water with hose or sprinkler as needed. The hay/straw is normally left in place and I just mow it under or it biodegrades.
BTW, if you used hay instead of straw, you picked up some seed from it. Plan on eventually having to kill that off.
Now before you think you messed it up, spots with lack of seed are somewhat normal in a new area. It's common to have to over-seed the area for a couple years to get it to fill in fully.