You won't fail if you mess the first attempt up - unless you do something crazy, most examiners will give you another attempt. But you will be required to complete it safely and succesfully.
The PFL is one of the things that many students stuggle with - and unfortunately there is just no substitute for lots of practice, in different wind conditions (i.e. strong winds, calm winds), and from different starting altitudes. It's the best way to build your confidence up.
If you have any doubts about the PFL, your course instructor will be more than happy to spend time with you to practice some more.....