The reason you're getting mixed messages is because each hospital has it's own policy, and there's an awful lot of ignorance amongst medics about GBS IME.
They'll give you IV ABs during labour for the GBS. As long as you've been in labour long enough to receive a couple of doses (about 8hrs, I believe) then there would seem to be little reason to keep you in(unless you want to).
If you don't get IV ABs in labour, some hospitals have a policy of insisting on a course of IV ABs for the baby, regardless of whether they are 'high risk' or not.
I argued against this, and we compromised on 24 hours observations (they'll take the baby's temp and heart rate every 4 hours to check for signs of infection).
I must point out, though, that I'd previously had a baby while GBS +ve who was unaffected, so I knew I was low risk.
If you don't get enough IV ABs in labour, and as it's your first, personally I'd either stay in for 48 hours of observations, or get them to teach you what to look out for. Unless you're high risk, I wouldn't allow routine IVs for the baby.
Take a look on the www.gbss.org.uk site and the Patient info section on the RCOG site then make up your mind.