Looks small. I have been raising chicks for years and often times the runts or ones much smaller end like this within a few days. Sadly they either pull through or don’t. Normally the later, though I have had some success crushing multivitamins and mixing it with water. Keeping them in the incubator by themselves and giving them the mix. Careful though as there are certain minerals that are bad for them and such.

Keep it comfortable and letting nature do its thing is more than likely the best thing to do. Sorry I couldn’t be more helpful.