。
I really need to get my watch fixed.
Literal
Truly watch [object-を] fix-receiving-must.
Two stacked constructions. ~てもらう is the benefactive auxiliary for 'receiving the action' — the speaker is not fixing the watch themselves, someone else will fix it on their behalf. ~なければならない is the compound 'must do' construction (literally 'if-not-do, it-will-not-become'), the most formal-flavored of the several Japanese 'must' expressions. The agent is omitted as always.