It doesn't matter how much or how little experience you have, your first landing in a new type, even if it's as small a change as going from old to new generation 172's will almost always suck. You'll get used to the newer 172's even if it takes a few hours. 18 hours isn't much, so it shouldn't take too long to work out the kinks. The only difference in getting used to new aircraft other than proper training is nuance.