Ovulating/charting issues

So I am FINALLY ovulating. Better late than never? I guess. It was Cd22 yesterday and I finally got a positive ovulation test last night - yep, night time - after I started cramping and couldn't figure out why. Took the opk test and sure enough. My problem is when I updated my glow chart with the results, it changed my expected period start date to 15 days from now instead of 10. I will probably start it sooner than 10 days (seems to be my running theme). I am just irritated that there is no way to manually change it back to the previous expected period start date (before I logged my positive opk test) so now I have to keep track on my Google calendar so I don't have AF giving me a nasty unexpected surprise. Grrr... Anyone else ever have this problem?