Here's how I would have written it. This is not for you to copy, nor does it mean that what you wrote needs to be changed. I just thought you would like to see how a native speaker would have described the event. In my own words:
I finally went down to the Tong Studio to sit for my graduation photo. They specialize in yearbook pictures and have several different graduation-themed backgrounds to choose from. The place was busy and they had one photographer on staff at the time, so it looked like the wait would be long, at least an hour or so. Fortunately, I didn't have to wait that long. About 40 minutes in, another photographer showed up.
I watched while various graduation props (caps, gowns, diplomas, and roses) were brought out, and the backgrounds displayed one by one. All for me to choose from. The background I chose was the one with a small podium next to my college flag. It looked real, like I was actually at my commencement ceremony, but that feeling of excitement that started to build steadily in me abruptly stopped and turned into a feeling of forlorn when I noticed the family members in the room who had accompanied other students to the studio that day.