Yeah, I always found a few problems towards the end of Catullus' infamous dedicatory poem.
The main problem is the colloquial "habe tibi" which is used by a speaker indifferently and is often found in Plautus' comedies (e.g.Men. 690 'tibi habe, aufer, utere') and means, effectively, "It's yours, such as it is". It is a rather self-disparaging phrase which Catullus uses to heighten the modest nature of the introduction to his corpus - sort of, "have it then, I'm not really bothered about that". libelli is a partitive genitive dependent upon hoc, and adds all the more deprecation of his work, diminutive as it is. It is also very rare to have two indefinite pronouns (viz. quidquid and qualecumque) as one is obviously superfluous. But anyway, this little snippet amounts roughly to:
"Whatever sort of a little book this is, then, it's yours".
You should have put all of the latter line in - it's great since it doesn't scan. I reckon Catullus just went off the boil as opposed to any manuscriptual error!
p.s. are you from Britain?