Hi Kit, this is where you let Fib guild you gently. But the structure's rules have to followed, so yes, dump those extra threads. Remember, close counts. Another way to use Fib with blocks is 1 x A, 2 x A, 3 x A, 5 x A, 8 x A, 13 x A etc.
Sometimes I start with the width of the fabric I want, find out how many warp threads I'll have, divide it by the number of threads in a unit and then you know how many units you have to play with. So many ways to approach design.