You don't need coco if you are using this soil and add perlite. Perhaps you can mix the two successfully, but most growers grow in one medium or the other. The perlite is very cheap and simply keeps the soil loose and helps with draining. Coco is used in place of the soil and uses a different method of growing to prevent issues. Are you following a recipe for the soil? There are quite a few out there and some may be better suited for more advanced growers than others, which can make them complex to make and use properly. I'm sure some other members will chime in as well, and most have considerable experience and have made every mistake possible.
I use a mix of 80% Promix and 20% compost/manure, a handful of wood ashes, and regular 20-20-20 fertilizer (Jacks). This is super simple and will give you better results than you thought possible. You could provably mix the bagged soil in place of the compost and manure. This will keep you from wasting the dirt that you already bought.
Good luck and use patience. Don't try to grow the worlds biggest plants... learn how to grow well first, then it I easy to advance your grows without multiple sources for problems. If you want to use Coco, make sure to do a little research on it, especially mixed with dirt. Go easy on food, plenty of strong light, and good drainage, and you will have success. Good Luck!!