At the blackout time, some light had entered the box from the corner of the window, and I realized it too late. Do you think I'm in trouble?

If it was one time. Nah should be fine. If it was happening over many nights. then yes this could be an issue. Could be key word. Patch the hole with a few layers of tape and hope for the best.

It can cause trouble, depends on how strong the genetics of the plant are. Some herm easily and a little light leak could be enough to get them to throw out a few bananas, but often it's not enough, so just keep an eye on them for anything that looks like a male flower or banana in the bud if she's further into flowering.