If I contributed only $1,150 to my Roth IRA last year, yet TurboTax has me paying $69 tax on my contribution. As Roth is post-tax, why is there an additional $69 tax?

A 6% excise tax applies to any excess contribution to a Roth IRA. It would appear your $1,150 is excess, as 6% of $1,150 results in the $69 penalty.

If your modified adjusted gross income is above a certain amount, your contribution limit is gradually reduced. 

https://www.irs.gov/retirement-plans/plan-participant-employee/amount-of-roth-ira-contributions-that-you-can-make-for-2018