You already have the wrong mentality to dive solo, not to mention the lack of training and experience. Don't dive solo isn't one of those hard-fast rules like "Don't hold your breath while making an ascent", but it takes extra training and equipment. Others here are giving you good advice such as get training, carry a redundant air source, ect., but the only advice you should need right now is get the training!! Even PADI came out with a self-reliant diver course, so solo diving is becoming more popular. One of the requirements though is to have a minimum of 100 logged dives first.
One thing you should have learned in the open water course is plan your dive and dive your plan. That first solo dive was planned to dive with a buddy, and when he or she didn't show, you broke that plan and dove anyway. And it's not about just being comfortable in the water. You must be completely comfortable with all the emergency procedures and be able to do them as if they are second nature.
I'm gonna go jump off a cliff now, want to join me?? Everyone is doing it!!