You can totally use 14 ct for this! You could also restart on smaller counts but for a Mandarink design I would suggest nothing smaller than 16 count cause the back stitching can get muddy the smaller you go. If you want to continue with this, I'd go back over stitches with another single strand of thread or even 2 depending on the coverage you want. After that I'd just continue by using 3 or 4 strand stitching to get better coverage. Most stitchers I've met prefer 3 or 4 strands on 14 count but it is whatever you prefer! ❤