06 prius 113k miles with dreaded p0420 code

I recently bought an 06 prius with what i thought just needed a HV battery but turned out to need a battery and inverter but a few days later i got those both replaced. Now i’ve been driving it and the CEL keeps coming on in less then 50 miles for p0420 cat inefficiently. Is it really possible for a cat to fail this early? i tried to look at post cat sensor data but it seems to hang around .8v if i remember correctly. when i bought it the gas was a year old in it and it barely made it to the gas station misfiring and struggling due to the low octane so i shot a few gallons of premium in it and the misfires went away and ran fine so i went for a drive and it popped up so i thought maybe it was just the old gas so i drove it until the last bar started blinking then filled it up with 93 and cleared the code and within 50 miles it popped back up again! Could i be lucky and just need a sensor or is the cat really dead at only 113k miles?