You probably got one because it now includes mortgage insurance premiums.
You can amend your return to include the PMI amounts paid (the deduction for PMI was reinstated in February by Congress). However, it will only benefit you if you are itemizing your deductions and have tax liability left to reduce (after applying all other credits and deductions). You also don't need to do this right now. You have 3 years to claim a refund on an amended return.
Click here for instructions on how to file your amended return.
See this article for more information about deducting PMI as there are also income limits - if your income is above these thresholds then your potential deduction would be reduced or eliminated (and thus no need to amend)