Not sure, are you trying to download the 1950-CMW710-R3116.ipe or the 1950-CMW710-R3115P08.ipe? on the first one for sure there are BootROM (version 146 versus your 124), boot and system images.
Have you set the file attribute to M (Main)?
After that step, the Switch should start to self-decompressing the boot bin and system bin files (automatically extracted from the downloaded ipe file)...eventually it will be necessary to update the BootROM first too (if necessary, as in your case).