That sounds like an awful lot of weight to add to a prop that is that small. Is this for an electric power system? Are you sure you are balancing it correctly?

If it is that far out, you may just want to toss it and get a replacement. Most prop manufacturers' props are pretty much balanced off the shelf. APC, for instance, rarely requires balancing. A quick check of the balance of a new prop should show that it is pretty much dead on.

If the prop moves a little bit on a "magnetic" balancer, then don't worry about that. It will be fine.