Hello. Again, I am by no means anywhere near a pro. I have read so much over the last 2 months, I feel as if I took an accelerated graduate crash course on weed growing!
That said, the stretching seems to me that the plant is reaching for the light source. Perhaps you would be better off leaving indoors with 18/6; a dark cycle is important for the processing of the nutrients and such. Although they are autos, I went with 18/6 during veg stage and switched to 12/12 for flowering mainly for saving some money on electrical bills. How high is your light to the topmost part of the plant? I tried to keep my light at 18". Since I was in a small closet, I did not expect the plants to get as tall as they did which necessitated some LST. I was afraid of the stress since the plant was already flowering, but it seems to be doing well. My Amnesia stopped stretching and is now beginning to fill out at the bud sites. She will be small due to the 1/2 gallon pots I went with.
This is my best plant - Blueberry - Last week @ 3 weeks of flowering. You can see some of the string I used to tie the stems down.
As far as the P4P soil, I can’t recall where, but I believe someone speculated it was Fox Farm Ocean Forest soil. Not sure. But the Happy Frog is very popular. Many folks who use it. Just do a search and you will find many posts with soil info.
Keep us posted. Continued luck.