Hi, first an apology for failing to find a more relevant thread to put this question in:

MAD-LHR-SFO in a few hours (3/7), on BA 125 ticket.
MAD-LHR operated by IB.
Had earlier chosen a bulkhead aisle seat (15J) but prefer a window, I see 15A is "X" on EF.
If I try to OLCI (to try to grab 15A) it takes me to IB (as first segment is on IB).
On the IB app seat selection screen I have selected a seat for MAD-LHR but it won't display my already chosen seat for LHR-SFO.
If I proceed with OLCI, through IB, I'm worried something will go wrong and I might lose my 15J (15A>15J>any other seat).
Am I being overly cautious?
Thank you!