Terrifying End of the First Day but he was found

So we all know how neurotic and nervous I am about Carter's safety. Keep that in mind as I relate the following story. Carter was supposed to walk out of the school with his friends and stay at the fence where I would be waiting for him. Of course I was nervous about it because after all I'm neurotic and don't like the idea of him exiting the school doors but I decided that now that he's in first grade he needs a bit more independence and after all if he stays in a group he should be able to make it 50 feet to the fence where I'd pick him up. I got to the school several minutes early to make sure I got the parking spot right next to the fence so that he could easily find me. After several minutes I began seeing kids come out of the school so I was waiting and watching anxiously to see Carter come down the sidewalk. I waited what seemed like a long time and then suddenly saw his 2 friends come by but no Carter. I got out of the car and started looking for him. His friends had not seen him. I walked into the school and to his classroom but it was empty. I started panicking since I had already scanned out in front of the school and called his name several times. As I was going back outside I saw his kindergarten teacher from last year and asked if she had seen him and he had gone to her to say hello and then had gone elsewhere. She immediately started looking for him in one direction while I went the other. She found him on the other side of the school. Carter's excuse was that a girl had found him and told him she was riding home with him and to go this way. We were giving that girl a ride home today because her mom was without a car. However, Carter had specific instructions to stay with his friends and was misled by another child. When Mrs. Brown brought him to me I told him that he needs to always listen to my directions and not to someone else's. It upsets me that he'd disregard my instructions and be so easily led. I was so completely terrified and crying. I wanted to run trying to find him but I knew there was no way that I could because of the baby. The fast walking back and forth in and out of the school had left me out of breath and I was so scared of Carter being missing and of the effects this stress was having on the baby. Thank heaven for Mrs. Brown who stayed calm even when I was panicking and found Carter and brought him to me. She had Julie do an all call in the school so Carter was paged over the system while we were looking for him. This was a first day fiasco and I was absolutely terrified. When I couldn't find him with his friends or in his class or out in front of the school I instantly started thinking the worst. I was looking at the big vans and thinking how he could have been grabbed and thrown into one and I would never know. I looked ground level hoping that I wouldn't find his little body crushed under a car. I had every horrible thought imaginable and couldn't stop thinking and praying to please let me keep my child. I was utterly terrified. I have never had a more scary moment in my life. I have never "lost" Carter before. After all, remember we don't even use babysitters. The time felt like forever and I was so scared I couldn't even be really mad when he was found. I was more angry at the situation and circumstances than at Carter though I'm starting to feel more angry with him which must mean the fear is subsiding. I feel like I haven't been able to breath ever since this happened. I'm still all shaky and have bursts of crying and major anxiety. I am seriously considering revoking letting him walk out of the school like normal childen. I'm thinking of making him stay in the office until I come get him. Overeaction or justified? I don't know. Matt and I will have to discuss it this evening. I'm so thankful his K teacher found him and so thankful he's okay. I felt the most helpless awful feeling in the world when I was looking for him. I cannot imagine what the parents of a missing child go through and I pray that I never have to experience this immense fear again.