Welcome. My name is XXXXX XXXXX it will be my pleasure to assist you with your tax question today.
First of all, do not worry about this even though it may be upsetting to you.
If you realize that your tax preparer made some mistakes, my best advice to you would be to amend your 2011 tax return to correct the mistakes and submit it as soon as possible. It is always best to come forward with correct information to the IRS, rather than the IRS confronting you about it. You may want to consider consulting with a CPA or Enrolled Agent so he/she will be able to either attend with you or in your place.
If you do end up owing additional taxes, there will be penalties and interest due. They will not make you an offer at the audit. If you do end up owing additional taxes, penalties, and interest, you will be able to request an installment agreement to pay the amount due (if any) or you can make an offer in compromise for a different amount, which the IRS can accept or decline to take depending on the circumstances.
Please let me know if you require further information or clarification.
Thank you and best regards,