I went to a sleepover last week and during the night we did the salt and ice challenge and the next day it started going a really dark purple like a bruise and after a week its still there and its getting quite itchy, my mum does not know and I don't really want her finding out but I'm starting to get concern about it scarring? My friends went away and she did hers a lot longer than mine, I'm also starting to get tiny spots around the burn which is starting to worry me. Can anyone give me some tips on how to help keep the redness or itchiness down? Would be much appreciated :)

Quite possible as you have given yourself frost bite..
Only time will tell.

Tell your mum. You could still end up with a nasty infection and definitely a permanent scar, especially if you get no medical help for it.