However ive noticed that underneath theres one wee bit of hair that is still "warm" looking- not as "platinum" as the rest.
Rather than call up and have fixed as it is only small- just been missed i think, if i keep my "silver shampoo" on that bit for a wee while longer should that sort it out??? Xx
No, it will need to be corrected to be the same colour, even with the use of silver shampoo (which irons out the brassy tones) it will still be a different colour to the rest of your hair.
Did you do it yourself? Carefully put a bit of toner over the missed bit, or, if it's not noticeable, leave it alone. If it was done by a hairdresser, they would normally be happy to touch it up for you and not charge for it if it's their mistake.