It is possible for the Quickbooks admin to use my own ID in order to register transactions?

If they have, or know your login information, they can do it.  

Welcome to the Community, @JAM007.

Thank you for choosing QuickBooks Online.

Just_me is right. To prevent other users from using your own ID to log into QBO, we suggest not to share your username and password.

You can restrict the permissions to prevent unauthorized users from entering transactions. 

Here's how you manage user roles and permissions:

1. On Settings, select Manage users.
2. Locate the user you want to Edit and choose a user type.
3. Click Next.
4. Choose the access rights for the user and click on Next.
5. Select the user settings, if applicable, and click on Next.
6. Click Save.
7. Ask the user to relog in to QuickBooks Online to see updates.

I'm adding this article as a future reference to monitor the activities done by the user: Use the audit log in QuickBooks Online.

If you have future inquiries about QuickBooks Online, don't hesitate to let us know about it. Have a great day ahead.