The dose recommended for rabbits in BSAVA Small Animal Formulary (which they are supposed to get their information from) is: dogs 0.1mg/kg, rabbits 0.3 - 0.6 mg/kg and up to 1.5mg/kg short term every 24h. All the rabbit vets I've worked with have said that's the lowest analgesic dose of 0.5mg/kg. This means that they don't think that anything below that provides adequate pain relief or any at all in rabbits. Normally, they are started on a higher dose to kick in the antiinflammatory response. If you're only concerned about inflammation and not pain, you can start off at higher ranges and go down to 0.3mg/kg maintenance regime, but I've never considered that effective for much. I've had rabbits started on doses been 0.6mg/kg and 1.5mg/kg. Rabbits tolerate 1.5mg/kg well for several days on a row and, unlike in carnivores, this dies not cause blindness on them. It's metabolised completely differently in rabbits and the risk of kidney failure is i believe low. There is also anecdotal evidence that some rabbits prefer a higher dose (0.6mg/kg) given twice a day. In theory better serum level would be maintained this way. I've had an old gentleman bunny, severely arthritic, where it interfered with his mobility, who was on 0.6mg/kg twice a day (so 1.2mg/kg total a day, that's 12 times the dog dose) for about 3 years, and every time this was reduced or if he didn't get a dose, this really noticed in him. He had several blood tests and his parameters always remained normal, so it did not affect his kidneys or liver, and if it helped him, that's all that matters to me.
0.5mg/kg is approximately 0.33ml/kg, 0.6mg/kg is 0.4ml/kg, and I work in these measurements because it's a long-term treatment, and weight can fluctuate (especially in older rabbits), making it necessary to adjust medication. You should have been given a normal syringe with millilitres marked up on it, not the dog one that comes with the drug.
Is your vet rabbit-savvy? Are they exotics specialists? I've never been given such a low dose, and I have a lot of rabbits on this drug. You can always call RWAF and ask for details of bunny specialist vets in your area (RWAF hold a register of them) and seek a second opinion if necessary.