editing of short passage

One morning a few years ago, when I arrived at the office I was surprised to see a few of my colleagues from another section there. I was also surprised that I was among the first staff members to reach the office. I was usually among the last.

A few minutes later, I thought that it must be a public holiday and that the staff from the other section were there to supervise the labourers who had to work that day. I checked my pocket calendar and, sure enough, it was a public holiday.

After that I returned home. I did not tell anybody, even my parents, that I had been so forgetful. Neither did I inform my colleagues the next day about my mistake as I was afraid that they might laugh at me.

Hi Contrex

Many thanks for your help.

Here's what occurs to me:

A few years ago, when I entered the office, I was surprised to see a few of my colleagues from another section there. I was also surprised that I was among the first staff members to reach the office. I was usually among the last person to reach the office. <----- should be "last people"

A few minutes later, I thought it must be a public holiday and the staff from the other section were there as they had to supervise the labourers who had to work that day. To confirm my belief, I checked my pocket calendar and, true enough, it was a public holiday. <----- comma after "were there"

After that, I returned home. I did not tell anybody, even my parents that I had been so forgetful. Neither did I inform my colleagues the next day about my mistake as I was afraid that they might laugh at me <----- comma after "parents"

Many thanks, Brandon9000, for your help.