There is no law that says you have to have a place in day services
When you become 19 and move into adult services your statement of needs is not enforceable. This means you do not just get the help and support you got as a child. You have to ask for it. There are lots of people who want to use day centres and so if you get a place at one it may be only for a few days a week. On those days there are lots of other people there too. There will usually be a choice of activities but it may not be possible for you to do the things you want on the days you go. If this happens, TALK to the staff.
It is your right to have a plan that is right for you, but your responsibility to tell people if you are not happy. And staff are not always mind readers but they do want you to be as independent as you can be and have lots of choices.