Missing parts in a Lego Mindstorms box
If you have a brand new set, and a few parts are missing, you should definitely contact LEGO Customer Service, so they can send you the parts you are missing.

New sets with missing parts
We’re really sorry to hear that something was missing from your new LEGO® set. We do our best to make every set perfect and we take it very seriously when a faulty one sneaks through. Don’t worry though, we can send you the parts you need!
Please click “Missing Bricks” on the Bricks &amp; Pieces section of our Customer Service site to order the part you need to finish your set.
If you can’t find what you’re looking for, make sure you include a complete description of the part (the part number provided in the inventory page at the back of the building instructions is useful) along with the set number. Once your part is on its way, we’ll send you a shipping confirmation email.
If you’ve lost some bricks over time, please remember to click “Buy Bricks” instead.
-- LEGO Customer Service FAQ

Just tell them the part numbers you are missing and they should send you the parts for free.