Stylee, one thing I would advise is if you tightened up, the workout should have stopped then.
As you may or may not have known, Charlie became known for not having written workouts and used each day to monitor what athletes would do. If he felt they weren’t ready for work that day, something else would be given. If workout deteriorated, workout would be stopped.
Also, it appears some of your back and forth might be arm action, or possibly lack of ab strength. I’d recommend spending a week or so at a slower pace working on getting into better position on your runs and then from there, increasing speed.
This take a step back to make more progress has worked well for my athletes in the past.