Simple thing is - are you using a big enough cuff?- it should cover at least 2/3rds of your arm (long axis, before anyone gets smart) - using too small a cuff can give erroneously (high) figures.
If the cuff is the right size, and you are consistently getting such results, get it checked by your friendly nurse a few more times. If still high, best to see your GP for futher evaluation.
Good luck!