dont know why camera has made it dark??
This is a common problem in photography due to the way that a camera’s light meter works, which is the part that figures out how bright the scene is and tries to calculate an appropriate exposure.
The solution most cameras have (this includes most cameras built-in to smart phones) is manual ‘exposure compensation.’ If your photo turns out too dark (or too bright in different cases) look for a button or setting called compensation, or even just +- . Add a little bit of + and try another shot.