Thanks Calliewag, Wendy and Jazzgirl.
Just taking a quick peek on Sunday before going out.
Chanbers does give 'shape up' = 'to be promising' (see Ixion - earlier) BUT this is more in the way of 'to develop' and certainly does not translate to 'promise' = 'shape well'.
I hope the setter has not, successfully, misled us! lol
I have had great faith in this particular 'magazine' crossword until recently, when a large booboo occurred. That was just a wee slip. Hope this is not another.