Game camera smaller than preview camera

When i’m in the editor the camera shows everything ok, but when i play it the camera gets smaller

What do you mean “smaller” ?
Are you confused between the “scene” view and the “game” view ?

When you press play in the editor and you don’t have a game view displayed, your scene view turns into a game view.

Check this page : Learn game development w/ Unity | Courses & tutorials in game design, VR, AR, & Real-time 3D | Unity Learn
USING THE UNITY INTERFACE 1/2/3

If it’s not helping, please be more specific.