I did it! And it only took a couple of hours.
I took a pattern that I got at the thrift store for 29 cents and altered it slightly (the purple markings are my alterations to the pattern).
Then I traced it onto tissue paper so I can use the original pattern still if I want later.
I pieced it together, sewed and hemmed the dress. Until finally it was done. And it only took about two hours start to finish, including little interruptions by my precious ones.
So that’s it. The birthday dress is complete. It was so easy that anyone could do this!