How do i feel more involved?

My step mum is pregnant with my dad and hers first baby together. As my mum and dad aren't together i only get to see my dad every other weekend. I feel like because of this i wont be involved very much. I want to be there for all the silly little things that people may not think of as important. Mainly just shopping for the cot and painting the room and things like that. My step mum is very close to her sister and i don't want her to go with her and not me. What can i do so that i don't feel like i need to be involved all the time? or how can i make them realize i want to be there and help with everything? Thank you in advanced :) Shannon xx