Honestly, it is going to be difficult for you to tell at that size unless, 1) you have others to compare to, and #b they are at least L3.
There's no visual difference in the sexes until they are L3 (this doesn't apply to all species, but works for Creos). At that L3, I can grab my handy-dandy 10x loupe & pen-light & look at the last abdominal segment. The female will have one large segment at the end (and sometimes you can see a little 'V' notch in it), the male will have a divided segment, giving a higher segment count if you are the segment-counting type.
From around L4 on, it's easy because the male Creos will develop thicker antennae (but again, it's helpful to have a larger group with both sexes, so that you have something to compare to).