1099R

I have recently retired and received a 1099R form. Federal Income tax has been withheld  from my taxable amount on the 1099 R form. This is my pension that I am currently living on. When it asks what I did with the money, and I click on cashed out, it adds a couple thousand dollars to what I owe. Why would I owe more taxes on the money I'm expected to live on when taxes were already withheld from the taxable amount?