Yes, I sew the front seam and then push the seam allowance to one side and edge stitch to hold it in place. I only do that on the front piece with this pattern.
The example looks like this alternate pattern that uses different fabric for the front and the back. In that case, you could easily edge stitch both as well as choose to only interface either front or lining (I recommend trying the lining fabric Linda, I have found that decreases fabric moving during the inhale). For this pattern though, the interfacing ends up on the entire piece which when folded includes both front and lining so you end up with 2 layers of fabric and 2 layers of interfacing.
I’ve used the other pattern when I haven’t got enough of the fabric to use it for both sides but I do prefer this one for both fit and speed of assembly.
@AIMR, this note is for the other pattern with different fabrics used for front and lining and doesn’t apply to this one. I notice you are edge stitching at the sides and then again about 3/4" in. If it’s because the seam allowance gets fiddly inside the mask and makes either turning or inserting the elastic tricky, I have been cutting the seam allowance a bit larger and the ironing it open flat before sewing the top and bottom curve. Alternately, if you trim about 1/2" from the lining fabric only, it moves the seam allowance to the inside of the mask so the fold is only comprised of the front fabric and that seam allowance doesn’t interfere at all. I will make a video for both patterns and link them in the original post. We’ve just been so busy here with other things lately…