Congratulations OP.
Try not to worry too much, the home visit will be an informal chat at home about you, your history, your partner, what plans you have and how you're planning to cope with a baby. Yes they will be looking at the home environment, but from a 'is it safe' viewpoint, rather than is it immaculately clean. They want to work with you to support you if that's what you need.
Be yourself, remember that they're there to help and support you if needed and above all else, be honest and co-operative. They want the best outcome for you and your baby, the same as you do.
You'll always hear stories of people claiming that SS took their children. In reality, this isn't common practise, is very difficult to do legally and involves a long process whereby parents are given opportunities to make changes to ensure the safety and wellbeing of their kids, yet either don't engage with services or don't comply with child in need and child protection plans and that's why the law then has to become involved.
In this situation, it's not just a social worker who decides what happens to that child - case conferences are held, with parents and all professionals who are involved with the child and it is at conference that plans are made to help the family and/or decisions to remove the child are made before they then go to court. It's not an easy thing to remove a child and there are lots of people involved in the process, not just a group of evil social workers who have an agenda. Ultimately, it is the decision of court to remove a child based on the evidence they have been provided regarding the risk to the child and the willingness of the parents to comply and make changes. Children being removed isn't a common thing as the focus of social services is supporting families.
Ultimately, social services want happy, healthy children with happy, healthy parents at home, together as a family unit.
And those bashing social services and the process, shame on you. No process is perfect and it is ever evolving but trying to frighten someone, who is already vulnerable, into being fearful of SS is pretty poor; especially when the opinions you have are based on second hand experiences and what you've heard in the press (of which you'll never know the full story). If you'd ever sat on a safeguarding children study day or ever been to case conference you'd have a different view of those who work hard to protect children.
Anyway, OP, apologies for derailing a little.
As it stands, treat it as an opportunity to gain extra help if you need it, or an inroad into help if you need it in the future, try not to see it as a negative thing.