At the beginning, you know just enough to get yourself into trouble, but not enough to get yourself out of it again :-) The trick is to go beyond that point.
If things go wrong with your child theme, then you simply rename your child theme folder with FTP. If things go wrong with Customizr, you simply rename your Customizr folder. (You can find these in the wp-content\themes folder.) In each case, WordPress will no longer find the theme it expects and will switch you to twentyfourteen. From there, you can put things back together again.