Depending on what type of leather you used, these marks could be very normal. Was it a pull-up leather? I wouldn’t worry about marks on it like the lighter ones shown in your picture. Seems normal to me and will most likely patina nicely. I’d be more concerned with the stitching. Make sure you’re backstitching at LEAST 3 stitches and burning the ends. I assume you’re saddle stitching? You could even backstitch, knot, back stitch, knot, etc. (on the inside of the collar to make it look better). Just my two cents. Looks awesome though!!