I had two of my kids hospitalized in the adult ward when they were teens because there was nothing else available in our area. It turned out to be a positive experience for both of them. They did see some things that surprised them but didn't upset them. Just the usual with people having problems. For our daughter it was the thing that helped her get past her struggles and she has been well for 11 years now except for a bit of post-partum depression which was treated and she did well. Our son also found it positive, he was hospitalized again when he was 18. Again it was a good experience overall. He was six hours from home but our daughter happened to work in that particular psych ward.
I struggle with depression and have for 22 years. I always consider the hospital my safe place where I can go if things get to be too much. It sounds like you need to be there now and you have made that choice. It will be okay and remember they will understand you are scared and afraid.
Best wishes for a speedy and full recovery.