You will be sent periodic reminders via email as the delivery date for the group gift approaches. The reminders will include the goal amount and the amount contributed to the gift as of that date. If you feel that the goal will not be met, you can invite more friends to contribute, send reminders to invitees who have not yet contributed, or even extend the delivery date.
All of this can be done from the Group Gift Management screen. A link to this screen is included in each reminder.