Thank you for your question, and thanks for requesting me directly.
You can deduct the taxes that you actually paid during the year, so if you only paid three months of real estate tax, then that is all you can deduct.
You deduct tax in the year you pay it because you are a cash basis taxpayer
If you have deducted too much, then yes - you should amend your tax return.
Typically, though I see real estate taxes paid once per year, not in installments.
Is there anything else I can assist you with today? If not, please rate me positive so that I may receive credit for assisting you today