この気持ちが冷めないうちにがんばります！！「鉄は熱いうちに打て」といいますから。

！！「」。

I'll work hard while this feeling is still fresh! As they say, 'strike while the iron is hot.'

Literal

This feeling [subject-が] not-cool [while-うちに] will-do-my-best!! 'Iron [topic-は] hot while [at-に] strike' [quotative-と] say [reason-から].

冷めないうちに 'while it hasn't cooled down' — うちに marks a window of opportunity. 鉄は熱いうちに打て is the Japanese equivalent of 'strike while the iron is hot' — a proverb about seizing the moment. がんばります with double exclamation marks shows strong determination.