Previous 3 Months Average

Hi,

I'm trying to create a measure which will display the average of the last 3 months

This is what I want is have as a average over the last 3 months. For example, April's % will be an average of April, March and February. January's % will be January 2021, Demember 2020 and November 2020 etc

I tried searching on the forums and came accross this piece of code 

3 Month Rolling Average Fall Through = 
var threeos = CALCULATE (
    AVERAGEX ( VALUES ( 'Date'[Month/Year] ), [Confirmed]),
    DATESINPERIOD ( 'Date'[Full Date], MAX ( 'Date'[Full Date] ), -3, MONTH )
)

var threewith = 
CALCULATE (
    AVERAGEX ( VALUES ( 'Date'[Month/Year] ),[Fall Through]),
    DATESINPERIOD ( 'Date'[Full Date], MAX ( 'Date'[Full Date] ), -3, MONTH )
)

return

IFERROR(threewith/threeos, BLANK())

This results in what it looks the next 3 months rather than the previous so I don't think that's right. Here's a screenshot

I'm struggling which is why I came here

Here's the PBIX: https://www.dropbox.com/s/4pbc79tpo9yg59a/help.pbix?dl=0

Any questions let me know

Cheers,

Mike