。
I got stage fright up on stage.
Literal
I [topic-は] stage [attributive-の] on [at-で] became-nervous.
あがる has multiple meanings ('rise, go up, finish'), but 舞台であがる is idiomatic for 'to get stage fright, become nervous in front of an audience.' 舞台の上 ('on stage'). The verb captures a specific performance anxiety — the kind of freezing that strikes when you're under the lights.