
600mg in a 24 hour is not insignificant...but not at all high. Mine was 6000+ when it was checked a week prior to delivery and I've heard of others higher still...but not long after that my kidneys really started to struggle and almost stopped producing urine altogether which was what ultimately got me delivered at 33 weeks.
Any spot test will produce results based on the concentration of your urine at the time. The lab won't care, they can still do the test...but first morning urine is always preferable.
Are you going public? You should be seeing a dr now you have a diagnosis if you're not already...when do you go back? Ask them to repeat the test, which they probably will be planning to do anyway.