The school of shifting Rooms and heavy Keys

"I dreamed I was back at my old school, but everything looked slightly different. The hallways seemed much longer, and I couldn't find my classroom. I kept checking the room numbers, but they kept changing whenever I looked away. I finally found a classroom and walked in late. Everyone turned around and looked at me, but I didn't recognize any of them. The teacher handed me a test and told me I should have finished it yesterday. I sat down and looked at the first question. It was about something I had never learned. Then suddenly I was outside on the school playground. I was carrying a backpack that felt incredibly heavy. I opened it and found dozens of old keys inside. I had no idea what they were for. The school bell rang, and everyone started running toward the building. I followed them, but when I reached the door, I couldn't remember why I was there. I woke up feeling like I had forgotten something important."