Hi Alex,
In the Smith Cart product setup screen populating the "URL Keywords" field does not remove the page name from your URL, but will replace the default.aspx with the value you enter. For example, in our store we entered "DNNShoppingCart" as the URL keyword for the SmithCart module and as you can see in our live store the resulting URL is as follows:
https://www.smith-consulting.com/pd/P...
If you want to completely remove the page name or the aspx extension you will need to use the iFinity URLMaster module or configure your IIS with some URL rewriting rules.