well - you obviously spend a lot of time in that region.I got blindsided by their expansion... how would I know if there was information in their news a few days prior to them being in my system? lol
beside galaxy map state filters, checking faction states and station news around is a good habit playing the BGS - it allows you to get an idea of what is happening.
but especially as you were actively carving out a retreat for your player faction getting in, i think checking for potential expansions into the system would have been the way to go (if you attempt something crazy like this)- and keep any faction in range below 75%.
if you would have checked, the expansion going pending and active would have allowed you to cancel the retreat, until that other player factions expansion is over.
but really - what you were attempting is hard in itself; some of it worked out impressingly (forced retreat is already hard with random traffic); you learned a ton. i somehow have the feeling you are starting playing the BGS from the extreme end of it, by bringing you and your group into a situation where you start with "master class level" of forced timed retreats and directed (non-)expansion in a region with other player groups active and probably a bunch of random traffic as well.
i applaude such bravado, i really do. as long as you enjoy it and see it is a self-imposed challenge.
if it is "just" about getting a faction for your player group ingame, simply revoke the old and resubmit a new application, add 3 systems to it, at least two of those with 6 factions or less.