Quiltler’s queen is 90 by 95 inches. Four inches of overhang makes 98 by 103. A batting package printed Queen is often 90 by 108 — that 90 inch side is already smaller than a 98 inch batt. The length (108) is fine; the width is not. This is the most common “I bought Queen batting for a queen quilt” surprise.
A King package around 120 by 120 covers 98 by 103 with room to square up. If you refuse to buy King, piece two Full batts, or cut from a roll, and still measure 98 by 103 before you load the quilt. The batting calculator is the same math with editable overhang.
Backing for this bed is how much backing for a queen quilt. Design the top in the queen quilt designer. King batting is how much batting for a king quilt.