Don't want his mother in the delivery room with me.
No, it's not wrong if you don't want her there. It's your personal decision and you shouldn't feel pressured to have people there if you don't want to. It just ends up stressing you and that's not good in that labour situation. Also I think the nurses/doctors/midwives don't want too many people in the room either.
Just let her know in a nice, kind way, that you prefer just your boyfriend to be there with you and if she can please understand and respect your decision.