I'm sorry about your issue. I had once ordered a bracket which seemed to be very thin and got a refund. This is not normal and i think it's a bad production, maybe it's already broken after production due to inhomogenius material or too small production dimensions.
I'm sorry but you'll have to write a ticket directly to shapeways with your order#. I think you'll get a refund. Hundreds of customers have no problems, because the bracket normally is very stable and should endure the bending force a several times more than you need to put it on the gimbal.
Once again sorry for your issue.