A levels

can I still choose business as A level if I didn't choose business as gcse. If yes, will I be okay or behind ad I didn't choose as gcse

Yes you can. The reason being not all schools offer gcse business, and making it an requirement for all A Level business courses, would not be good.
There will be overlap between gcse and A Level - but that just means working a litter hit harder. As people who have studied the gcse, will not remember all of it, and they will have to revise it.
They are relearning something they previously knew, so need to spend less time on it.
You will be okay