You will get there, use area QNH or AWIS QNH from somewhere within 100NM and you will add 50' when you didn't have to.
My bolding...
Was mentioned previously but obviously some people haven't been picking up on it or are being told incorrect things (not having a go AS2A, I just want to point it out again as I still hear lots of people getting this thing mixed up), but for an Instrument Approach you cannot use QNH from a place within 100nm; doing this is for all other operations is an altimeter setting rule. The Application of Aerodrome Meteorological Minima section "supersedes" this:
ENR 1.5-5.3.1
Prior to passing the IAF, pilots are required to set either:
a) the actual aerodrome QNH from an approved source, or
b) the forecast Terminal QNH, or
c) the forecast area QNH.
Absolutely ZERO mention of QNH from within 100nm for your approach.
Is it likely to kill you? No, but it isn't the correct way to fly the approach.