This depends upon many factors. For example: The crime you were convicted of; Whether you completed any of your community service and, if so, how much; Whether you were previously granted one or more extensions of the time to complete your community service; Whether you returned to court voluntarily and on time, or if you were picked up on a bench warrant; Your prior record, if any; and of course, which court you were convicted in and who the judge is. If you have not already done so, you need to consult privately with an attorney.
The court may find you in violation of your probation. In that case, the court has a wide range of options.
a) a slap on the wrist, and more time to finish your community service, to
b) revoking your probation and sentencing you to jail.
If you have an attorney, contact him right away. If you can get an extension to complete it, do so. Don't wait. The court may not drop the hammer on you, so don't delay.