The app script is still in my template after the removal of the app

The Shopify uninstall process does not allow us to access your store once you hit the 'Uninstall' button.

We cannot remove the app script if you haven't disabled the app before. So we always suggest disabling the app before uninstalling it. In this way, clean removal of the app will be ensured.

If you didn't disable the app before uninstalling you will find a line similar to:

 <script src="//app.shippingratescalculator.com/js/core/main.min.js?timestamp=1646902639&shop=example.myshopify.com" defer></script>

at the end of your theme.liquid template. It won't harm your store, but you can remove it safely, just delete that line from your template.