Help with sweatshirt seam

Hello! I hope I'm posting this in the right place. I've been sewing for about a year or so and have been making mostly dresses for myself. I have a 100% cotton heavy sweatshirt fabric that I'm making a dress out of. Because of the stretch, I'm using a zigzag stitch. However, no matter how narrow I make the stitch, it always shows on the right side of the fabric on the seam. I tried a straight stitch and it did the same thing. Any tips for resolving this? I've attached a few pictures with a narrow stitch to show the behavior. Thank you so much!

Shoot, I'm not able to attach the images. 

Haha, I was able to save one of the images as my profile picture so you can see there :) 

Hi, oh that's a pain! It looks like an issue with your sewing machine, is it doing this on other fabrics?

I haven't tried recently on other fabrics but I'll give it a shot! I ended up doing the zigzag and then top stitching and that seemed to help. I also changed the needle from 90 to 100. Thank you for the reply! 

Are you using a ballpoint or stretch needle as well?

Hi! Yes, using ballpoint needle. 

Has your machine got a "lightening" stitch? - the picture of the stitch looks like a lightening flash and is used for knits/jersey 

Hi! Yes, it has a lightening stitch. I can give that a try too! Thank you!