I believe that we did ok with out agile mentality. Each day we retroed and discussed the next step or two and how we were going to attack problems.
When we got together, most of the work was done driver/navigator. This had its benefits and takeaways. We all knew the code quite well, but it ate up a lot of time when we could be working on other things.
If we had a further goal- maybe a month or so out, I can see how an agile mentality would be beneficial. Attacking things and regrouping as necessary.
With the short timeline we worked in, though, it seemed like we were just working on the next thing in the rubric.
I also believe that expertise is required for true agile implementation.
We had no idea if writing a code was going to take 20 minutes or four hours making it hard to estimate where we should be at in any particular moment.
I appreciate the reflections here on your group's process and attempt to integrate agile practices. Since you didn't specifically answer the questions on describing agile, waterfall, and retros, I would recommend you spend some time thinking about how to describe these components as you prepare for interviews.