The passive heatsink I fitted on my M.2 drive had two sections that screwed together, i.e. a top section and a bottom section. The M.2 drive was sandwiched in between the two metal sections, with a thermal pad underneath and a thermal pad on top.
If the plastic latch on the motherboard is fouling on the heatsink and you don't mind a bit of DIY, judicious use of a Swiss File could be used to remove extraneous metal from the end of the heatsink.
Be scrupulous when cleaning fine particles of metal left by the file before fitting the M.2 drive or offering it up to the motherboard to see if it fits. Keep the thermal pads well away from the area when using a file. They'll pick up metal swarf which could cause a short circuit.
If you don't want to "mangle" the heatsink to make it fit, buy a different heatsink. They're not that expensive and it's worth doing the job properly.