HSA contribution section will not let me enter post tax contribution only if excess contribution

You can enter the contribution you made outside of payroll.  

Here is how you can enter personal contributions to an HSA in TurboTax Online:

• Click on Federal Taxes,  Deduction & Credits
• Choose "add/edit" HSA, MSA Contributions
• You will see a page titled "Your HSA Summary" which will show any deductions already computed from your W-2  
• Choose Edit, Check the box for HSA, Continue
• You'll now see a screen that says "Here's what we have so far" with the information from the 1099-SA, choose "Edit"
• After the entry screen for the amount distributed, double check the number is accurate, continue and when it asks "Did you spend your HSA money on medical expenses only?" answer "Yes", if accurate. 
• Choose done and continue until you get to a screen that says "Let's enter your HSA contributions"
• In the box "Any contributions you personally made (not through your employer)" Here is where you enter the amounts you did NOT contribute through paycheck withholding.