I have mistakenly purchased an app from app store, Can i refund it and get my money back?

This is primarily a user-to-user support forum; other Apple users like you. The instructions in Request a refund for apps or content that you bought from Apple - Apple Support describe how to make a request to get your money back. If that doesn't help, also see the following from the same support article:

Get more information about refunds

See how long refunds take.

For more information about refund requests or for other refunds that you can’t request on reportaproblem.apple.com, contact Apple Support.

You can try by using the following instructions: Request a refund for apps or content that you bought from Apple - Apple Support