僕は校長先生のまえでおちつかなかった。

。

I couldn't stay calm in front of the principal.

Literal

I [topic-は] principal [possessive-の] before [at-で] could-not-settle.

校長先生 ('principal') — 校長 + 先生 (honorific). おちつく (落ち着く, 'to calm down, be composed') in negative past. まえで ('in front of') — 前 + で (location). Written in hiragana rather than the usual kanji 落ち着く.