Beginner.....follow the stats?

[dangerousuk]

I play mainly low level sit and go's and after learning about sharkscope through this site was able to check out my stats. I have not been using pokertracker or similar software nor keeping records of my profit and loss, so to see it laid out how much i had lost etc was quite an eye opener.
One of the biggest shocks was the amount that my ROI changes from day to day and that most the week it is -ve but on saturdays rockets upto around 65% (from 57 games). The number of games played on each day is similar (between 40 and 60)
My questions are these
1. How accurate are these stats? Are these artificial stats created by either the website or the relatively small sample size?
2. Should i stick to playing games on saturday? The money would be nice but my poker 'aim' is to be a winning player 7 days a week - would it affect my improvement as a player sticking to what appears to be easier games?