If you want to preview branching logic and get the Congrats Page, you will have to make sure and answer all fields AND choose the correct answers as you set in filters.
Ethnio will cleverly not show the Congrats version of the thanks page to anyone that leaves blank fields in their screener response. It's a way that we guard against speedy fakers trying to participate in your research. Also use a unique e-mail each time you fill out the screener to test the branching logic and want to see the Congrats page.
One small detail to keep in mind while editing the Congrats page: the second block of text is automatically made a link, based on the 3rd party URL you entered above, so there's no need to manually make a link in the text: