Basil, I had a similar experience this morning. It's so scary when they bolt, especially if they're heading towards a road.
This morning Pip and Lurcherboy made friends with a lovely retired greyhound. I let Lurcherboy off first and they had a nice play, but Pip was a bit woofy, so I kept him behind me and ignored him until he calmed down. Fortunately, she was a very confident, but sweet dog and approached him really carefully. After gentle introductions I let Pip off and they did a few deferential play bows and bouncing about, but then Lurcherboy and the greyhound decided to run and Pip panicked. He bolted towards the main road, with greyhound in hot pursuit and like Fitz, it took what felt like a lifetime for him to come to his senses and hear me calling. Didn't help that because I panicked I didn't grab the whistle.
I was just calling him, so am so relieved that he came back. He got such a huge gobful of chorizo and cheese and a huge big fuss when he made it back to me.
Fortunately the owner was really friendly and hung around while all three dogs reintroduced themselves nicely and the greyhound and Lurcherboy had a few more plays, so it ended positively.
Pip also said a nice hello to the cocker that ran all the way across the field and scared the life out of him a few weeks ago, having been introduced to her properly a couple of weeks back, so that was another relief.
Both dogs are covered in mud and exhausted and Lurcherboy has managed to tear his stopper pad. 
Sally, that is so cute!
I had to laugh when Pip ran into the swing the other day. He used to be able to run under it, so went full Lurcher-pelt and nearly knocked himself silly. He pulled up short and stood there shaking his head, looking totally stunned. Daft mutt! 
ITRC, why don't you book just a couple of 1:1 lessons to give you more confidence and keep going to puppy classes alongside.