Hi
Since the proposal to pay an additional sum of Rs150 per square feet for floating members and Rs22 Per square feet for fixed members has been proposed by court appointed mediator will be construed as a compromise agreement between parties.
A compromise agreement is NOT legally binding (unless and until you are a signatory to the agreement)
You may choose to disagree with compromise agreement and appeal against the compromise order in the same court.
Since technically the property is registered in your name and also that you have a possession certificate, it appears that at Rs22 per square feet for fixed scheme members, it might be the cost effective option to get your building completed.
The builder(society) is NOT entitled to ask for additional sums in future and instead will be asked to contribute their own reserve funds on the grounds that a compromise agreement once implemented will not be entitled for Renegotiation or reopening .
Hope this information is useful