fix: sandbox command (#7728)

Author: kita3222

src/fragments/gen2/quickstart/create-amplify.mdx

@@ -43,7 +43,7 @@ Now [configure your AWS account to use Amplify](/[platform]/start/account-setup/
 For the backend, we're going to start a cloud sandbox environment. Amplify gives every developer a personal cloud sandbox environment that provides isolated development spaces to rapidly build, test, and iterate. When you're working with a team, each developer will have their own personal cloud sandbox. In a new terminal window, run the following command:
 
 ```bash showLineNumbers={false}
-npx amplify sandbox
+npx ampx sandbox
 ```
 <Callout warning>Do not use cloud sandbox environments in production.</Callout>