Crochet Shawl “Evening Glow”

Hello, I have a question right off the bat....In the first row, you close with a treble crochet in the third chain stitch from the starting chain. But then I end up with a rounded beginning instead of a straight line....in other words, a triangle.....I hope you understand my question and can tell me where I’m going wrong...thank you...M. Düngel

Have you tried contacting the author?
I suspect the “rounded shape” will disappear as you continue crocheting

The way you describe it, this creates a loop—or a “curve”—at the beginning. I strongly suspect that several more stitches will be worked into this loop. That’s why the loop is needed—simply to provide enough space for the other stitches.
The triangular shape will form as you continue crocheting. Just give it a try and crochet a few rows as described in the pattern. Even without knowing the pattern, I’m still very sure that it will turn out to be a triangle.