Drive away, entering plain, but go too far? (9)
I believe the answer is:
overshoot
'go too far?' is the definition.
(to overshoot is to go past)
'drive away entering plain' is the wordplay.
'drive away' becomes 'shoo' (shooing is a kind of driving away).
'entering' means one lot of letters goes inside another.
'plain' becomes 'overt' (I've seen this in another clue).
'shoo' placed inside 'overt' is 'OVERSHOOT'.
'but' is the link.
(Other definitions for overshoot that I've seen before include "Maybe miss the green" , "Go past the mark" , "Go too far" , "Go extra distance" , "Go beyond the mark" .)