I think you are miscounting your days. 28 days is all days, not trading days. A tip on 3 Jan would have an opening price on Mon 6th January.so will expire on Sunday Feb 2 which is effectively at close on Friday 31 January.
You are definitely not alone in tipping a stock which has gone on even further after the competition. Luckily real life trading isn't restricted by those rules so hopefully you're either sitting on a nice profit or have banked one.
