22 is the width, 80 is the length. On a typical mobo, a 42 would fit fine in an 80 slot (80 is pretty much standard for these slots for this reason). However, looking at the hardware maintenance manual for the Y700 you're out of luck. There's no screw hole to tighten down a shorter m.2 SSD, so you'll need to replace with an 80mm SSD.
The good news for you is it looks like its PCIe SSD compatible, and NVMe on top of that. So you can go wild and throw a Samsung 950 Pro in there and it will scream. If you want to stick with SATA to save some money, you can get the m.2 version of the Samsung 850 Evo.