wrong Month values showing

baneworth  The Month column is numeric, and your axis is set to 'continuous'

So it's showing all numbers in between (months only have 12, but that doesn't fit within base 10 numbering system).

Either change your axis to categorical, or use "End of Month" column from your date table (if you have one) as that will be a 'Date' datatype instead of 'number' and will behave with base 12 month system you want 🙂