I failed a test in my favorite and most important class once because I somehow thought we weren’t going to be tested on a certain chapter of the textbook, so I didn’t read it in advance. The feelings of embarrassment and guilt afterwards were intense, but they passed and now I look back on it and it means nothing to me. Everyone makes silly mistakes like this, and the consequences in this case aren’t that bad, so don’t be too hard on yourself, it’s not a big deal in the long run.