They're obliged to rectify any faults, which they appear to be doing, but any work they do should carry a further guarantee so get this in writing if possible. Successfully getting a refund may or may not be nigh on impossible - depending on how awkward you and the dealer are prepared to be respectively, i.e. Sitting on the road outside their forecourt waving a list of all the faults you've suffered to prospective customers may tempt them to take the car back.
Generally speaking though, I'd be tempted to get the AA/RAC/Independant garage to give it a once over (probably cost you £50-£100) and get anything dodgy sorted by the garage before the warranty expires.
Citroen C3 though? Bit mainstream, isn't it?