Maybe you should remove the covering from the greenhouse. could be too much heat.
I planted my tomato seeds 10 days ago and they have their first set of leaves already and look good. I have them under the heat mat and grow lights. The lights stay on 14 hour a day and the heat mat 24 hours a day. My soil was drying out vey quickly and I had to water very often and then someone suggested that I raise the plant holder off the mat and that seemed to work.
