Whats considered to much stretching

So for the last 6 weeks or so I would stretch for about 6-7 mins, but I noticed that I was losing gains I went from 8cm to 8.5 then back to 8. So I decided it was time to up the routine ,I did 15 mins of stretches left,right,up and BTC 1 mins each . When I was done my routine I went and watched TV but I was curious if I actually stretched my penis or not so I measured my flaccid length and it was 9-9.5cm so yes I did stretch I now this is not a permanent gain, but if I continue to do this will my body cement this kind of gain. Also whats considered to much stretching.