Whether to mix the 2 soils is up to you. Most likely can’t hurt anything. Be aware that this is how you learn. Do it and see what happens. 
Youre right Beware that’s all I’ve been doing I lost seven out of 17 so I guess im doing ok next grow will be a lot more better, I hope! As for the soil I put together plants seem to be happy believe me I know what a sad looking plant look like.