So my question is, should I have originally asked for clarification? Should I have assumed a right pattern and thus a left 45 entry to downwind of 12? Should I have entered the crosswind of 12 and avoided the 45 all together (seems ilogical to me)?
Very confused here....
I would suggest that not only should you have asked for clarification, it should have been almost an instinctive reflex to do so when you didn't hear a completely specified instruction. (...and I don't mean any of this to be harsh criticism, it's just that clear communications are so important to flight safety...)
I don't have my AIM in front of me here, so I can't check, but I wonder if you go back and look up a reference to what you are saying: "if no traffic direction is indicated and there's nothing in the AFD, to assume a left traffic pattern....
" you'll find that this is an assumption that applies to operation an uncontrolled field. I believe (but I'm always willing to be corrected) that it's not really applied to a controlled field because ATC is supposed to provide that information.
For a few decades now, "CRM" (Cockpit/Crew Resource Management) has been a big area of training. It's a pretty broad area, but the overview is that crew members are trained to use all the resources available in the most optimal way to enhance the safety of flight. It includes interpersonal issues like personality and communication, training issues like the interface between pilot and machine, and cognitive issues such as situational awareness, problem recognition, task management and overload, etc.
The concepts of CRM can also apply to single-pilot operations. Even with a single pilot you still have man/machine interface issues, task loading issues, the Aeronautical Decision Making process, communications (e.g. with ATC) and so on. The idea is still to use each resource you have available in the most optimum way when you need to solve a problem, fill a gap, keep your situational awareness as high as possible, etc.
In your situation, you had a gap - confusion about the pattern direction. Now, you're certainly aware of utilizing available resources, since you are aware that sometimes a pattern direction is indicated (with ground markings) or specified in the AFD, and if neither of these, then you apply the general "left pattern" rule of thumb. Given an uncontrolled airport, these pieces of knowledge might have been the only resources you had available at that moment to fill your gap.
But in your actual situation, I would suggest you had a much better resource that was not only available, but has high value and reliability, and is already part of a system specifically designed to "team" with you for the safety of your flight, and that's the controller.
To narrow the question down to your particular situation: given that you recognized you had confusion on the pattern direction issue, what was the best, most reliable resource you had to resolve that confusion? In the controlled field environment, when you're talking to the tower, if you KNOW you have that gap, and you have the choice of filling it with an assumption (which leaves uncertainty) or confirming with the controller (which "costs" nothing and guarantees a reliable solution), doesn't it make hugely more sense to use the controller resource?
My question (and please understand that I'm asking this gently, not to needle you, but to help you consider your use of the resources you had available): is there something that you thought was not right or appropriate about asking the controller for clarification in this case? Was there a source of hesitation that you felt?
In a way, I think you had a kind of an advantage... A 'dumb' pilot might have just stumbled into the pattern one way or the other and never know or care about the ambiguity in the controller's instruction. Maybe he gets it right "by chance" and nobody ever notices the difference. But you got step 1 right: you recognized that there was a missing piece - whether the controller didn't say it, whether you just didn't hear it, the point is that you recognized that you didn't have that piece. The next step is to consider the resources you have available to you, and use them in the best, most reliable way to fill that gap. And another critical piece of the whole picture is to be able to recognize and get past any human obstacles (hesitation, embarrassment, communication issues, personality issues, etc...) that might get in the way of that most optimum resource usage.