we can't see your return. a guess would be that your withholding was based on you not retiring. retiring and then have lower taxable income but higher than required withholding would produce this situation.
...another thing to check if the refund is really unreasonable?
Edit any forms that you entered data into that had tax withholding entered...sometimes the tax withholding $$ are mis-keyed with an extra digit, or a decimal place in the wrong position and you didn't notice it when you entered that data. Double check the numbers on each software form.