I was waiting in front of my PC for my English teacher to start our lesson not realizing he had cancelled our lesson at the last minute.
I had my computer open and ready to start our English lesson, but then I checked my email and realized my teacher had cancelled the class just before we were supposed to begin.
ーI was waiting in front of my PC for my English teacher to start our lesson not realizing he had cancelled our lesson at the last minute.
「先生がレッスンをドタキャンしたのを知らず、PCの前でレッスンが始まるのを待っていた」
to wait in front of one's PC で「PCの前で待つ」
to cancel one's lesson at the last minute で「レッスンをドタキャンする」
ーI had my computer open and ready to start my English lesson, but then I checked my email and realized my teacher had cancelled the class just before we were supposed to begin.
「コンピューターを開いて英語のレッスンを始める用意ができていたが、メールをチェックしたら先生がレッスンの始まる直前でキャンセルしたことに気がついた」
to check one's email で「メールをチェックする」
to cancel the class just before we were supposed to begin で「クラスが始まる直前でキャンセルする」
ご参考まで！
I was waiting in front of my computer, unaware that I had been canceled on at the last minute.
この状況では、「ドタキャンされる」に当たる表現として「canceled on at the last minute」が使えます。
例文: I was waiting in front of my computer for the online English lesson, unaware that I had been canceled on at the last minute. Only when I checked my email did I find out.
このフレーズでは、「unaware」は「知らずに」を意味し、状況に合った表現になります。
カナダ 
アメリカ合衆国 
