Considering you have no civil engineering background (let alone structural) and do not work in the profession, I think you've done pretty well for yourself so far. Structural Engineering is not an easy subject and I don't think it's the easiest available option for this exam.
My undergrad had a heavy emphasis on structural analysis and design. I have been a structural engineer for the last year at my company, with the remaining time (3 years) spent designing roadways. Most of my colleagues suggested I take the Civil Transportation PE rather than the Structural. I even know some full time structural engineers who have skirted the Structural PE for an easier pass. Personally, I still took the Structural PE. In hindsight, it might not have been the smartest decision on my part. At the end of the day, a PE is a PE. There is no distinction once you've passed, at least from what I can tell; someone please correct me if I am wrong. I'm pretty sure I worked harder than I had to and there are undoubtedly more references for the Structural Depth than any of the other Civil disciplines. In the end it worked out for me but it served no purpose other than to prove a point to myself.
It's great that you are interested in the subject. But on the other hand, I personally think that unless you plan on working in that field in the future, you may be doing yourself a disservice. The calculations are inherently more complicated compared to the other disciples and there are many more codes & references. You also have to recognize there are many ways you can go through a whole question thinking you are right and still wind up with a trap answer. As noted in the post above, the distinction between ASD and LRFD is a good example of this. You can spend a whole 6 minutes on a problem, then forget a reduction factor and you would have been better off guessing from the get go.
If you plan on taking the structural exam again, make sure you have all the references. As you saw, the most recent PM section was very code oriented. The morning is also crucial because the type of problems that will be asked are much more predictable and less demanding. The more points you can get in the AM, the more slack you have for the PM.