OK, you have this all setup wrong going by your image. You dont add a retroarch core like that. Add retroarch itself as the emulator, call it Retroarch as well, this then gives you options that you wont have in the image you show there. When Retroarch is setup as a emulator, you can then set whatever core you have downloaded for whatever system you want, see below.
Which gives you access to the associated platform screen, which will list all the systems you want to run with Retroarch, as well as what core it is to use, which can be changed to whatever core you want.
CPS3 wont be in that list as its not a system, its just arcade, so you will need to scroll to the empty cell at the bottom of that list and manually add that system, making sure you call it EXACTLY what you called it when you imported the roms, and in the second dropdown that appears set it to "scrape as" arcade. Its also worth noting that CPS is just in a mame romset, so you dont need a separate platform if you have a mame romset
I would highly recommend taking a look at our youtube channel, where we have tons of step by step tutorials on setting up all sorts of systems with all sorts of different emulators.