Assuming you want to hook it up in Parallel like this:
B-B-Load-B-B
Yes each side will only carry half the current, however should it become connected like this:
B-B-B-B-Load
then you will be undersized and the cables will overheat.
For the amount of cable and its cost I would stick to using the full load rather then praying no one mis-wires it and risking a fire. If you have any plans for expansion I would in fact recommend upsizing a bit.