Downs screening

Sammie
Little bit of background my little boy is 4 months old and I am 11w3d pregnant. I had my dating scan yesterday and opted out of screening but after thinking about it further I think I'm having second thoughts. Don't get me wrong either way it wouldn't make the slightest bit of difference to me I would still want my baby and love it the same I just feel that maybe I should have some idea this time as I already have a small baby to look after and maybe the time to wrap my head round it and prepare would help. I know these test are never 100% I just don't know I feel different and am worried. My question is will they let me change my mind I'm in the uk. And would you if you were me? Thanks ladies x