Are you saying that most of bootstrap is working, but the text-center class is not? Pretty sure the text-center class has been called that since the dawn of time, so if that isn’t working then something isn’t right. Can you post your head code here, remember to use the correct code formatting.
Also, how are you running the file, did you try using a local server. I don’t really know netbeans but it’s super easy in VS Code using the Live Server extension.