〜てしまう / 〜ちゃう end up doing; do completely (often with regret)
Examples
すみません、少し緊張してしまって!これからはもっと静かに挨拶します。あ、これ、私の捜査手帳です!
I'm sorry, I was a bit nervous! From now on I will greet you more quietly. Ah, this is my investigation notebook! (N5 lesson 1)
なるほど!もし脱ぎ散らかした下駄を踏むと、足元が滑って転んでしまいますものね。
I see! Because if someone steps on scattered clogs, their footing will slip and they might fall, right? (N4 lesson 2)
前から手前に引いても全然動かないんです……敷居を越える前に車輪が壊れてしまいそうです!
Even when I pull it toward me from the front, it doesn't move at all... The wheel feels like it's going to break before clearing the step! (N4 lesson 4)