Hitting a target zone for backpacking is a common difficulty, no matter what the target weight or volume. It is even more difficult if committed to lightweight backpacking. Consider the following possible courses of action. Many are obvious, but others might provide some new ideas.
Granted, this is a long list covering a wide range of suggestions. Nevertheless, it should give you a lot of ammunition to work the problem. Consider going back and circling those suggestions that have the most promise.