Lots of women have it and in the vast majority of births where Mum is positive, it doesn't have any effect. A lot of women don't get tested and a lot of them will be carrying it. Please don't worry. Make sure you tell your midwife, it may affect your birthing plan but most importantly, try not to worry. It's good you know to make sure you can minimise any risks.
This is from NHS:
Risks in pregnancy
If you have group B strep while you're pregnant:
your baby will usually be healthy
there's a small risk it could spread to your baby during labour and make them ill – this happens in about 1 in 1,750 pregnancies
there's an extremely small risk you could miscarry or lose your baby
What happens if you have group B strep
If tests find group B strep, or you've had a baby that's been affected by it before, you may need extra care and treatment.
You may be advised to:
speak to your midwife about your birth plan – they may recommend giving birth in hospital
contact your midwife as soon as you go into labour or your waters break
have antibiotics into a vein during labour – this can significantly reduce the risk of your baby getting ill
stay in hospital for at least 12 hours after giving birth so your baby can be monitored – this isn't always necessary