How can I check for a collision before or during FixedUpdate()?

I am making a physics-based marble game and am having trouble getting the marble to jump properly. Right now, I think that it jumps twice when I press the jump button. Here is the code for jumping.

 function FixedUpdate () {
     if (Input.GetButton("Jump") && canJump) {
        rigidbody.AddForce(Vector3.up * jumpForce,ForceMode.VelocityChange);
        canJump = false;
     }
 }
  
 function OnCollisionStay () {
     canJump = true;
 }
  
 function OnCollisionExit () {
     canJump = false;
 }

I think that the first time the marble jumps, it is still in contact with the floor, so OnCollisionStay reverts canJump to true and lets it jump a second time. Because of this issue, I want the code to check for collisions before the if statement. How can this be done?