It sounds like you clicked "run" before the sandbox environment was done deploying. If you wait a minute or two and press run again, it should redeploy with the current changes. If after awhile it still doesn't let you deploy again, you can check your application logs in the sprinter portal under the environments tab to see if there are any errors.
"Run" will deploy your application to your free application sandbox in the cloud. "Run locally" will deploy your app locally on your computer so you can test.
And sometimes the above will still not work. You then have to file a support ticket.