If your conditional green card was obtained by marriage with a US citizen, you and your spouse should apply to remove the condition 90 days prior to the expiration date. As long as you applied for the removal of the condition, even your temperary green card will be expired, you can still wait in the US. You need to remove the condition to get the permenant green card.
My website has more information in this regard -- runanzhang.com.
Runan Zhang
Attorney at Law
