高中英语短文改错

I have a very embarrassing experience this evening.have 改 had
I saw a boy at a bus stop when I was on my way to home.to 去掉
Though I saw him from behind,but I was sure he was a friend of me whom me 改 mine
I hadn't seen for a long time.I gave him a tap on the shoulders shoulders 改 shoulder
with my umbrella and shouted to him at a same time,a 改 the
He turned round,completely taking by surprise.taking 改 taken
Unfortunately,he was not my friend but a complete stranger.I was terribly embarrassing,embarrassing 改 embarrassed
for I didn't know how explain to him,explain 前加 to
I could only say in a low voice,"I'm so sorry"After that
I walked away as quickly as possibly,possibly 改 possible