Stuck on a simple line chart

The issue i’'m facing is very simple. For personal knowledge i am coding a small app to track child growth. I am learning bubble since 1 week via Gregory John’s youtube videos and some practice. I apologize in advance if i did something stupid.

I have in a database a table of all the percentile values until the 24th month.

And in a different section of the database i am trackign each child’s growth.

The main issue is matching the x axis for both series. For example in the chart below i purpusefully skipped some months hoping to see them “backfilled” but this this not happen. Of course i realized that i am using different dates, on one side i have months since birth and on the other i have actual measurement dates. In the screenshot i marked two children A and B. The chart refers to child A

What is the best way to convert measurement date to months from birth?

The second issue i have is to backfill lost data. I may forget to record a measurement for one or two months and i will just see data pulled forward in that case.

The below are the settings i used, this is driving me nuts since 3 days.

Overall, is there a more efficient way to setup this database?

Thank you