I am very concerned today as I discovered whatsapp has access to my google drive.
Does this mean whatsapp can steal my google drive data with this access or is it restricted only to a specific folder?
If you go to Google My Account Permissions and expand "WhatsApp Messenger":
View and manage its own configuration data in your Google Drive
View and manage Google Drive files and folders that you have opened or created with this app
I am not an expert on Google Apps permissions, but the wording would indicate that it is limited to files WhatsApp wrote to Google Drive itself: "opened or created with this app".
If the google permissions page states access to Google Drive (and doesn't limit this to a directory) it must be assumed the app can access anything stored there.
If you view this an issue you should suggest to the WhatsApp developers they modify this to only require you to share write permissions to a specific directory with them.