Hi
you could get the job to fail using something like
if datepart(dw,getdate()) != 1
RAISERROR (N'Error Incorrect Day', 16, 1,N'number',5)
this would fail on ever day but 1 and not proceed to the next step, unless you specify it to do something on failure i.e go to a dummy last step and exit cleanly, it really depends on what you want to do
Hope this helps