Raycasts have no thickness. It's a test for collisions on a line from vector A to vector B (from the raycast's origin to the cast_to
vector).
You haven't shared your code but probably you just need to normalise the cast_to
vectors and then multiply it by a scalar.
Something like this: cast_to(Vector3(1, 2, 3).normalized() * ray_length)
That'll preserve the direction and allow you to control the length.