0.3 CC is acceptable although I'm not sure how you got that reading. If you use a 10mL water sample, your readings are always in increments of 0.5 and if you use a 25mL sample, in increments of 0.2.

(A CC reading of 0.5 or less is ok. If it goes over 0.5, then you'll want to take your chlorine up to your shock level.)