Claudia -- You're the second person to contact me about this, and it seems that Google has completely revamped how their forms work. I'm still trying to figure out whether my approach will be possible with the new forms. Meanwhile, I'm recommending that folks use legacy forms, which will continue to be supported for an unknown amount of time.
You can create a new legacy form by logging into your Google account, and then going to: drive.google.com/spreadsheet/n...
The other alternative is to use a database, and I'll be posting more of those examples, as well.