How to make wbs Videos

I'm GREAT on the decomposition portion of the WBS...thank you. Where I'm losing traction is on the cost estimation of tasks. For example, if my total budget is $8.1M and I have 3 main project activities (A,B,C) composed of 22% of remaining contract dollars, 28%, and 34%. My problem is that there is 16% project manager admin costs in there as well. Does that go into the structure? Plus, there is a contingency of 4%...BUT it is included in the admin costs. No matter how I calculate it, when I check my work, I do not return to quite 100% of my budget! I'm wondering "which" costs beget the others? Do I subtract out all admin and contingency BEFORE I go on to estimating the major activities? Or, is it the other way around?

Finally cracked the nut between WBS and activity list. Both seem to cover the same areas of scope but define scope slightly different (deliverable based vs actions needed to complete those deliverables) THANK YOU!