By default, when you click on the New Worksheet button (Standard Toolbar), Origin loads the Origin.OTW template. You can modify this behavior so that clicking New Worksheet opens your custom template, instead.
The easiest thing to do is to simply modify the Origin.OTW worksheet template:
Open your modified template and choose File:Save Template As... from the menu.
Save Origin.OTW in the User Files folder.
Now, clicking the new worksheet button or opening a new project will load your customized worksheet. However, if you would prefer not to overwrite the Origin.OTW template, first save your custom template with a new name, then do this:
Select File:New. This opens the New dialog box.
Select the window type from the list box -- in your case, this will be Worksheet.
Select your custom template from the Template group. You may need to browse to your worksheet template using the browse button to the right of the Path box.
Click Set Default.
This changes the default template that is associated with the New Worksheet button on the Standard toolbar.
Sorry for the English instructions but I am sure that your English is better than my German.