Ignore the CAD. Even with 7+ years of working in solidworks, nothing I design is ever as the CAD says. I have taken to designing to roughly 5% under the limit. This seems to get me close once you include wiring lights, bolts, all the cable ties and electrical tape you use to lock things down. Even when the finished pieces weigh exactly what the CAD says they should somehow when its all together its always heavier than it should be.

Maddox is right BTW about the Alu and Hardox. However, if you feel better with Alu, go for that and then move to Hardox at a later stage.