Running

Good work! I think there's a bit of trial-and-error when it comes to getting the intensity right, because one of the aims is to be able to complete a full session with each hard bit being the same pace. (This really helps get used to race pacing.) But you should also be able to do it whilst keeping good form. If you're consciously changing form in a forced effort to up the pace, try to ease off just a touch, and concentrate on keeping your cadence ticking over nicely. Over time, getting used to doing interval and tempo running not only gives you a marked improvement in cardiovascular fitness, it also helps to improve your running economy, as your running form naturally adapts to operating at a faster pace as comfortably as possible. Another popular way of thinking of "tempo" or "threshold" intensity is comfortably hard, but hardly comfortable.

I could only do three sessions, not four. It was meant to be 7/7 on/off but I could only manage five minutes for the fast part.

Well done! It's still beneficial training. As others have said, it won't get easier but you'll get more accustomed to pacing and the pain :D

if you can’t run for 7 minutes at your threshold pace then it’s not your threshold pace. As I said before it’s the best pace you could manage for an hour, or in simple terms threshold is between your 10k pace and half marathon pace. As a rough guess your threshold is just over 5 min kms, so looking on Strava, at between 4:20 and 4:40 you were trying to go too fast.

What youve described is a vo2 max interval and a 5 min interval of this is a beneficial workout, but isn’t what was in your plan so don’t beat yourself up but go a bit easier next time!