Keep trying. It's harder than the Fun 27 challenge, although with the full range of skills Minimac gives you, it's not too hard.
On the other hand, try doing it the way I did *without* watching my replay first. (IE: 100% with 1 blocker, 3 builders and 1 basher) if you want a harder challenge. (Which still, to be fair, isn't *that* hard)