GetAxis Mouse X and Mouse Y returning high number values.

Just reading the documentation usually helps

The value will be in the range -1...1 for keyboard and joystick input devices.

The meaning of this value depends on the type of input control, for example with a joystick's horizontal axis a value of 1 means the stick is pushed all the way to the right and a value of -1 means it's all the way to the left; a value of 0 means the joystick is in its neutral position.

If the axis is mapped to the mouse, the value is different and will not be in the range of -1...1. Instead it'll be the current mouse delta multiplied by the axis sensitivity. Typically a positive value means the mouse is moving right/down and a negative value means the mouse is moving left/up.