For September it says I got 4.9 but when I search my shop it says 4.8, why?
You shops overall star rating and the star rating for star seller bits are 2 different metrics.
Overall star rating is the average of the last 12 months of reviews.
Star seller rating is a 3 month period of time.
@PsychicGoddess1 Star Seller is the previous 3 month rating - For Today, Sept. 1st, it's counting Reviews from June, July, August.
Your shops shows a 12 month average - 365 days, to the date.