I've just noticed that my tuner was set on 455 Hz , is this wrong? i read its supposed to be on 440?

so if so, i've been tuning wrong for a while now?
Guitar: Ibanez RGR321 EXBK

Amp: Bugera 6260 head + 4x12 cab
yep, it should be 440.

Your guitar has been in tune with itself (each string is tuned relatively to the other strings, so it souds right), but if you tried playing along with someone else (who tuned with a tuner at 440), you'd sound out of tune.