Unfortunately you're kind of stuck and those FPs are sunk until the building flips. Your options aren't great, but you can:
1. Use your spare FP from your bar to eventually flip it yourself.
2. Try to rally anyone else on the building and flip it together.
3. See if any guildies are in the target's hood and ask if they'll help.
Beyond that just chalk it up to a learning experience about being selective in which GBs to invest in. I certainly learned from a few of my mistakes like that.