まっちゃう
tamacchau

Godan Verb (ru)
Godan Verb (u)

The completive aspect (contracted form) - indicates completion or regret of 貯まる

1. To be saved up/accumulated (and now there's too much); To be full/filled up (and now it's overflowing); To have saved up/accumulated (with regret); To have filled up/overflowed (with regret)

Completed Action
Colloquial