No. You have to pro-rate the annual HSA contribution limit by 5/12ths, e.g., $1,438 ($3,450 times 5 divided by 12 for a Self-only plan), or $2,875 ($6,900 times 5 divided by 12).
It would be different had you been covered on December 1, 2018, because you could have invoked the last-month rule which allows you to use the full annual HSA contribution limit.
As it is, when you enter the HDHP coverage for only 5 months, TurboTax will calculate the appropriate limit.
