Based on the information you gave, it seems that you let the template grid retrieve the series data from the Microflow (MF).
The purpose of the Template grid is to iterate over all items of the List (returned by the MF).
That's probably why you see a new chart appear when adding new data.
I do not know which chart widget you're using.
But you could have a look at the Time Series widget (app store link)
This widget can be configured with a Microflow as data source. and then you should see 1 chart with all data.
(no need for the additional Template Grid!)