Great advice. My OW course wasn't that flash either and I did some pretty silly things when i first began diving, but I suspect like you, it was more out of inexperience and not knowing than purposefully putting myself or my buddy in danger. After all you don't know what you don't know.
I realised to become a safer diver and good buddy I had to take responsibility for learning more. I asked lots of questions of various DMs and experienced divers, re read and re read my OW manual, did countless searches on the net for articles, spent hundreds of hours on SB reading and asking questions, tried to imagine scenarios and visualize how I could respond and perhaps most important went diving as much as I could.
The article "g1138" links to is a very good article (thank you NWGD) I found it very helpful and also recommend you read it.
You need to take a step back and look at what happened, why it happened and what you could/would do differently. Diving isn't rocket science but its not to be taken too lightly either, sadly people do die and not just the inexperienced ones. As others have said until you have more experience maybe just concentrate on the diving and save the hunting for later. Im glad you both made it back ok, but dude it could have so easily been a much different, sadder story. Good luck.