One reading is nothing to be worried about - we all have the occasional high reading caused my many different factors, none of which is out of the ordinary.
You should be monitored over a period of time, assuming your blood tests come back 'normal'. If you do have consistent high blood pressure you will need to lose weight, exercise more, eat healthily and cut down on salt.
You may have to take medication as well.
Have a read here, which gives excellent advice:
http://www.patient.co.uk/showdoc/23068761/
In the meantime, forget about it. It is pointless worrying over one 'bad' reading - and will only cause your blood pressure to rise. :) Have the tests before you start to worry.