Google Sheets – How to Add Every Sunday in Sequential Order

So I tried using the simple formula:

=date(2019,3,10) 
=date(2019,3,10)+7
=date(2019,3,10)+14
=date(2019,3,10)+21

... etc.

But when I highlight the first top 3-4 cells to drag down and formulate the pattern it doesn't work in this case. My goal is for my sheet to auto-populate all Sunday's date in the year, even continuing to the next couple years in the future.

Any recommendations?