Ashey-P

Am having trouble on the mission "fly at 2500m for 200secs at mach 1". I can tick off the main part (flying at 2500m mach 1, 200secs) but then when I alter course for home to land, to fill the second part, it unticks. If I go over 2500m, speed up and time again etc to get the tick back, again when I change course it goes. Am I missing something? Will provide any information needed if I have to. Am not a tech-spert but would like to try and help get this sorted