The only possible thing that you did wrong here was be a little eager with the pace. Don’t be afraid to slow it down. Based on the data at the moment that average pace is a little quick. These runs, apart from the hills, should feel easy. My tip would be next time you go out for one of these easy runs, keep the pace to 6:10-6:30 per km. Then see how you feel at the end. If it feels much easier then you’ve found your current pace. I’m doing my easy runs at 6:00 per km right now and my current 5k prediction is 22:45 (PB 19:15). Slower is better sometimes. All that said, well done Mike on getting it done.