Normally, the
sum of the amount that your employer contributed to your HSA
and the amount that you contributed through a payroll deduction scheme would be reported on your W-2 in box 12 with a code of "W".
If the $100/month was withheld through a payroll deduction scheme, then you do not enter this amount elsewhere on the return; TurboTax will handle it automatically.
It's confusing, but the IRS refers to the employer contribution and your contribution through the payroll deduction scheme both as "employer contributions", and TurboTax has to follow the IRS' terminology.
The question of "Any contributions you personally made" refers to contributions that you made to your HSA outside of your payroll deduction scheme (if any).
