Get 100% to be sure (4,2,7)
I believe the answer is:
make no mistake
'get' is the definition.
Both the definition and answer are verbs in their base form.
Maybe they are linked in a way I don't understand?
'100 to be sure' is the wordplay.
I cannot really see how this works, but
'be' could be 'take' (taking is a kind of being) and 'take' is present in the answer.
This explanation may well be incorrect...
(Other definitions for make no mistake that I've seen before include "Get everything right" , "You can be certain" , "This is how to get full marks" , "get things 100% right?" , "believe me" .)