My first move would be adding something to that, with the aim of having your heart rate a little higher at the start of the first interval. Maybe your walk is brisk enough that another 5m walking would do it. It looks like that first interval is making a nice warm-up so maybe just double the first short interval and have the second one also be short instead of trying to do a long one there. ETA: That is: 5m walk to warm up, 90s run, 90s walk, 90s run, 90s walk, 180s run, 180s walk, 90s run, 90s walk, 180s run, 180s walk. I presume you know this and only didn't include the cool down at the end so we'd get more zoom on the intervals, but just in case: don't skip the walk at the end, you can hurt yourself by not cooling down as much as by not warming up.