Hi Renate,
It should allow you to extend it to BUP003. May be your BP was already created under role BUP003.
Sometimes when you try to open the BP, it shows under 00000 by default. You need to click the details and see if you can find BUP003 role there.
If this doesn't help. then please go ahead and delete the BP using transaction BUPA_DEL and then create a new one.
Thanks
Dhilipan