Is Natsu's half-dragon form his complete Dragon Force?
If we are going off of the Dragon Cry Movie, it was presumed, by loads of theorists on whether or not that was a glimpse of Natsu's Etherious mode, to be Natsu's Etherious Mode that triggered, but in all fairness, this is to be determined as a Dragon Force.
In short, no. This wasn't Natsu's Complete Dragon Force because there is no such thing as a complete dragon force. One of the best ways that support this is the Dragon Force page on Fairy Tail Wiki page,

Dragon Force greatly increases the damage done by standard Dragon Slayer spells, and grants the user access to more advanced, powerful attacks.
(from the first sentence under Abilities tab)

A better example that there is no such thing as a complete dragon force was when Sting used Rouge's Shadow and triggered a Dual-Mode Dragon Force.