Welcome to OSM and thanks for editing!
Here are a few tips for editing:

1) When drawing a parking lot area, try placing new nodes at every corner of the parking lot and make sure the line traces the outline precisely. Try to avoid cases where the line would cross grass, buildings or other objects that are not part of the parking.

2) I suggest you switch from the default background to 'CT ECO Orthoimagery (2019)'. It was made in spring when the tree leaves are gone and you can see the parking lot outlines under tree canopies better. 
Here is how to change the background: https://learnosm.org/en/beginner/id-editor/#configuring-the-background-layer

Let me know if you need help.
Cheers