The German language is "rechtsköpfig" ("right-headed" instead of "left-headed"), meaning that the grammatical properties of compound words are defined by its rightmost part/morpheme (this morpheme is called the "head" of the compound).
Therefore, in your example it's indeed a masculine word,
(der) Akt being this compound's head. Kontroll is called the "core" of the compound, which defines its semantic properties, i.e. it strongly influences that compound's ultimate meaning.
There are very few exceptions to this rule, mostly they are about derived compounds with prefixes like "ge", e.g. "Geschrei" or "Gejammer", where the (leftmost) prefix defines the word's gender as neutral.
(The fact that "Schrei" is masculine doesn't really lead to a conflict here, since those words are derived from the verbs "schreien"/"jammern", not from nouns.)