Welcome to the forum!! I agree with Gemm - it would be very helpful to know the size of the panel.
I often decide on the block size and the size of the outer border first. Then, I work backwards - add up the block size and border and then subtract that from the finished quilt size. Then, I would add inner borders to the panel so that my center is the perfect size - here is one I did years ago with that method (it is OK if the inner borders are not all the same width (inho)