Hi Joao,
I suspect you are using date values for the domain of the SteppedArea, which works a bit differently than you might expect since the steps are between values, so effectively, the first value doesn't count.
Two things you could do. First, convert all your date values to strings, so then they are discrete labels and each step will correspond to one value. A second thing you could do is keep the dates, but add a row at the beginning with a date that is where you want the first step to start.
Hope that helps.