hey Mate,
I have not used that potting mix but Searles is the one i used and TheGreenBandit, a mate on here, when i first started out growing December 2018. I used his thread hence searles potting mix with seed rasing mix in the centre its good for vege, and then a bit of potash for bloom. I also have tiny bit of that richgro phospous i might grind up also to give p and k. You are careful with the watering etc with her? She will pick up, i had one with my first grow, we called her little one , stunted and then took off like a bolt and caught up with her sisters and gave the best yield. If i get a stunted one ( got on atm) , and just hope it comes around.