I thought the max was only two cancels due to stamina constraints?
114xxSKRC (lose a bar of stamina) --> 114xxSKRC (lose another bar) --> whatever button you want.
Nope you can do 3 cancels on block with johnny, if you're losing a bar of stamina then you certainly aren't doing it fast enough, which means its not jailing anyway.
To answer op, if it comes out as a dash, look at your stamina bar and see if it flashes red. If it does, it means you aren't cancelling the first 2 correctly, and you're losing more stamina than needed. If it doesn't and you just keep getting dashes then its your execution on the third one instead. Either way, the only way is practice.
If i can give a terrible but hopefully accurate illustration, with | representing the stamina bar, and / representing where your bar disappears after a correct cancel, I can try to show you.
It should be; |||/|||||/|||||/|||.
You should be left with enough bar to dash cancel into another move if you were to cancel from your 3rd 114.
I don't know if that illustration helps but this should give you an idea of how to improve your cancels, besides that, just practice.