Hi Barry
I used to get really irked, in my youthful blinkered ignorance, when someone called my melodeon an accordion. For some reason, at least to me, melodeons were cool and macho and accordions were for effeminate nonces who played spineless, sloppy music. I hadn't considered the "button accordion". Or the many brilliant players of piano accordions. What a silly boy.
In fact at the time (although I didn't know it) I was playing a Hohner Vienna accordion - makes me blush to think how wrong I was.

[Although as recently as last week someone talked to me about my "accordion" and I felt that old pang of horror, the difference these days is that I don't try to "correct" them, after all, they may be correct - sheesh!]

It's all in the locality/region/country/continent/language/vernacular and any other variables you want to add.
My rule of thumb for naming these instruments will be different to anybody else's.
For what it's worth the name of 3 row melodeon fits the description of your instrument.
Oh damn, so does diatonic accordion. And button accordion.

Have fun with your . . . erm . . . instrument.
Martin