Sounds like a typical permission / execute error. What OS are you using? Are you following the exact instructions here -> https://docs.shopware.com/en/shopware-platform-dev-en/getting-started/installation-guide ?
Yes, I followed those instructions but at the time they didn’t make it clear that I was supposed to run the install command inside the container…probably obvious to someone with experience using docker but this was my first time using it. I see now that the page has been updated to make this clear 
I also added my user to the docker group so I didn’t have to use sudo. Everything seems to be working flawlessly now!