Just hang in there and he will adjust in a couple of days. Keep on him though. Don't let him think that bad behavior is acceptable. Let him be your special helper. My son is 4 loves this idea. He loves to help out. When I clean the kitchen he gets a Lysol wipe or two and wipes down whatever he can reach. In the livingroom he helps by dusting and picking up his toys. The hurry hurry hurry, fast as you can is his favorite game. Pick up something an run to put it away. If he helps you out it will keep him entertained and not so lonely.
We have also decided not to go the pre k route. But we do do "school" everyday. They sell those activity learning books at my dollar store. We have several of those that we work on. We have letters, numbers, shapes, basic math and a couple others. He loves them. He needs a little help usually but does really well. just something fun. He cannot wait to start school next year.