Not Exactly as Planned

Today I had a riding lesson. I put Tamara through her paces, walk, trot, canter, and learned to turn by rotating my shoulder and pressing with my leg. I dismounted without falling. So..I felt pretty good about the lesson! I curried Tamara, gave her cut carrots, apples and cookies and then my instructor asked me to put Tamara in the pasture. I confidently led the horse into the pasture, wondering how to put the horse in and secure the eight-foot gate at the same time. I led her in as I watched the gate swing open, and then removed her halter. I thought she would wander off to eat hay, as eating is her favorite activity. I was so wrong! Tamara saw the open gate and the opportunity to be free and walked right through the gate. I said "Whoa" and she continued on, even trotting a couple steps as she headed up toward the arena. I secured the gate so Creamer would not escape, and then wandered up to where Tamara was happily chomping on green grass. I tried to put on her halter, but must have put it on upside down or something, as it wasn't right. My instructor's dad came up and said, "Need some help?" I told him I did, and apologized for letting the horse get out. He responded, "Only need to say you're sorry if it's your 60th horse to get out." He told me that it's even worse if two horses get out. We walked toward the pasture and my instructor drove up, surprised to see us. She showed me how to hold the gate open, let Tamara go in on the lead, let the lead out and then have her turn toward me, remove the halter and then chain the gate. Something to work on for sure.