Leave your home/office now and go immediately to us consul in ballsbridge.
-try to phone first 6688777 but if you can't get through a real person, go anyway. Now.
No way you will get on flight if you have been denied authorisation.
Look again at every answer you wrote on your application. Did you write something incorrectly ? If so, you have a choice of resubmitting the application or going personally to consul and explaining.
If you are young, dont have much money(credit card/bank statments useful), a regular job (show proof of this), definite address over there then you may be screwed. a jobless young person with no guarantor/funds may have problems getting the O.K.
Now go and good luck
Can you change flight ?
I regret that no one else can really advise you except some Yank offical.
Even so-called experts (like I pretend to be as a travel agent) are,frankly , bewildered by the ever changing security regulations/procedure.
I am so sorry to sound pompous and perhaps this will help others reading this - getting the authoirsation before getting a ticket is a must. You don't need definite flight to get the authorisation.