the answer to the question is when in doubt - don't.
But it sounds to me that if you are in a 172 at idle power with full flaps and still not going to make the runway you are pretty high and that has presumably been developing for a minute or two.
Maybe you want to review your base and final technique and be more aware of what "picture" you should expect.
Last edited by Dave Gittins; 19th July 2012 at 11:35.