Will I be charged for the App that I downloaded accidentally from App Store?

If it is a paid app, yes.

M1 Mac mini, macOS 14.6.1;  Watch, series 7 GPS/cellular, watchOS 10.6; iPhone 12 Pro, iOS 17.6.1; TV 4th Gen, tvOS 17.6; HomePods, audioOS 17.6 and Airport Express w/ Airplay 2

Fortunately accidents are very difficult since it requires you to double tap the side button, followed by verification using Face ID/Passcode with the amount showing on the screen if there is a charge for the app.