This may simply be that they haven't done some pre-processing and that in a few hours OLCI will open fully for you. There have been some aircraft shuffling going on that route today for aircraft leaving LHR, so I don't know if that is having an impact tomorrow from BOS. Just try again in a few hours. Check also that you have a ticket number in the BA App. Normally turning up early doesn't hugely help here. It does look like a busy flight, but there is space in First so someone may be upgraded out of CW.