Well, they don't make them in .2mm increments for nothing.

But seriously, have you ridden the bike much with the new seatpost? Does it slip? When you put the seatpost into the seat tube, how snug is it? Is there any resistance at all, or does it drop in without even contacting the walls of the seat tube? If there's any resistance at all, you should be fine and you probably have the right size post. Even without any resistance, it doesn't necessarily mean you have the wrong size post.

At the top of the seat tube, where you tighten the seatpost binder bolt, look at the small slot and see if it's crimped noticeably inward at the top after you tighten the binder bolt enough to secure the post. If it is, then you may very well have the wrong size post. If the slot seems to be more or less the same width from top to bottom after the bolt is tightened, you should be fine. Again, the main thing is: does the seatpost slip while you ride the bike?