Not sure that your syntax is correct… the strapi starter CLI will take sew-ed as your local folder where the starter will create your final full-stack app, but you don’t have the last command line parm that would indicate what strapi starter repo (on github) to use.
I have an example of the syntax in my boiler plate starter for custom starter development here: GitHub - strapi-training/strapi-starter-to-customize (in the Misc Notes section)
(also, i recently tweeted about my recent video series about custom starters: https://twitter.com/monico_moreno/status/1386834033179602946 )