You should, I got a 58mm which was a bit silly... I got a bloody 58.4mm tamper about a fortnight later...
Edit: I didn't know a 58.4mm leveller actually existed til you said that... Balls!!! Still works tho', just needs a very gentle tap to knock the edges in before you tamp...
Which width did you get? I have a Classic too, and wondering if I should get the 58.4mm version to overcome the slight oversizing of the basket?