。
I've gotta go get vaccinated.
Literal
Preventive-vaccination [object-を] receive-[preparatory-ておく]-[must-なきゃ].
Packed casual speech. 受けとかなきゃ is a double contraction: 受けて + おく → 受けておく (do in advance, for preparation) → 受けとく; then the ~なければ(ならない) obligation contracts to なきゃ. Expanding it yields 受けておかなければ(ならない). Everyday Japanese casually stacks these contractions even in single-verb phrases. 予防接種 ('preventive vaccination') is the standard word for getting a shot.