I forgot I was logged in with my school account which is hosted by Google.
How do I delete my search history?
The following answer may not apply for a Google Apps for Education account but only for a normal (consumer) Google account.
As per the Google help page:
You can delete past searches, browsing history, and other activity from your Google Account. You're in control of what's stored in My Activity, and you can stop saving most activity at any time.
In your case, you should try to:
Delete activity from a certain day or time period
To delete all activity from today, yesterday, or another day or date range:
- Go to My Activity.
Remember: You first need to sign in to your school's Google Account.
- On the "My Activity" banner, choose More (the three little dots on the top right corner) and then
Delete activity by.
- Choose the day or date range.
- Select Delete.
- Confirm your choice.
In any case in the future you should always remember to not log-in your school account when you do not want your history recorded.