After finishing a job, be keen to get into shape (6)

I believe the answer is:

oblong

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'shape' is the definition.
(oblong is a kind of shape)

I don't understand how the rest of the clue works.

(Other definitions for oblong that I've seen before include "Log on B (anag.)" , "Rectangular two-dimensional figure" , "Elongated rectangle" , "Cab" , "Strip for planes" .)

I've seen this clue in the Evening Standard.

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