No it’s fine they all develop at different paces. My girls rolled the odd time but hasn’t for ages now and still can’t sit for more than a few seconds unaided, I’m not worried in the slightest
Mine’s sitting, but not rolling either. He’s on the heavier side and a bit “lazy”, always hated tummy time. Sometimes they can learn a new skill like rolling almost overnight, I’m sure it won’t be long and then we’ll miss the days when they stayed put 😅
My baby is 6 months next week and can’t sit yet but has rolled a couple of times independently. He keeps trying and usually only makes it halfway at the moment. They all develop at different times.
My baby does the same. He is not interested in rolling, but he sit up unaided