Do you see how much better he went forward when you circled also? I mean you, walked a very small circle so that you had life and movement on your feet and you face him and kept driving him forward. YOu can make that circle even smaller, and take great care not to cut too close in front of him. What I mean, is if you start circleing too fast, you end up getting in front of his shoulder and that is the body language for him to stop, or stop and turn the other direction. Or, he may feel pinched between you and the barrier and start chucking his head or acting up due to feeling squeezxed.
Never back up. you are backing up practically the entire time you lunge him at a walk. Walk (or rather pivot) on the same inside circle, and push the horse forward. Don't back away from him to get him to go around. He ends up lunging you!
If he leans too hard on the lungeline, give it a couple of short sharp tugs to remind him to not do that. When he starts looking outward, like he does, bring his attention back toward you. either hiss at him or kick some dust , or tap the ground with your foot, or ? get creative, but some small thing to interrupt that outward thinking on his part and get him to look at you and go , "What?", then direct him on.