This also happened to me! I put the bridge back on and it stayed upright but I could not tune it. After about half hour I was very frustrated. I took a closer look at lesson 3 and saw that I had the bridge on the wrong way. I had the downward curve of the bridge on the wrong side. I fixed that but I am having a hard time tuning it. I’m going to keep trying to tune it but if I can’t I’m going to have to take it somewhere to have it tuned.