If you had asked me before, I would have warned you off FirstBuy. The scheme is nothing more than benefits for housing developers, after some relatively tiny party donations.
The 20% loan from the government is a big chunk of the difference between the asking price the developers are slapping on and the real value of the property.
Even ignoring that, the restrictions that accompany properties sold under the scheme and the consequential trouble you will have selling it on, would be enough to scare me off. I've got contacts in the housing development game and they all realise how nasty the scheme is, but the type of people attracted to that game have few scruples anyway.
If you have any escape route from this, I would take it now. If not, start protecting yourself accordingly.