Read Exodus 5
God told Moses back at the bush that He would harden Pharaoh's heart, I think Moses forgot. I get the impression that Moses thought he'd just walk in and Pharaoh would say OK you can go. There is also the issue of going three days journey, it gives the impression that if Pharaoh let them go, then they'd come back. That would have been a better bargain. The people are angry and blame Moses for losing the straw, there is a disconnect here, they're not so upset at being slaves as long as they have straw? But all of this is of course for a specific purpose. Who will trust in God and who will trust in Pharaoh?