Hi userubboss:
When you create a new invoice, your default invoice template will be applied automatically. To confirm this, from the new invoice screen click on Customise on the bottom of your screen to see that your default template has been assigned (you only ever need to select another template if you wish to use a non-standard one).
If you don't see the one selected that you want, go to the Custom Templates screen, click the Edit drop down next to it, and choose Make Default.