Can I reject a boy for marriage even if my parents did Istikhara and it came out positive? Can I pray for a better proposal in my Dua?
Your marriage is invalid with out your full acceptance and agreeing. Your parents' Istekhara is for them to agree or not, but it does not bind you. You can go for Istekhara yourself or jointly with your parents if you are not clear and need guidance through an Istekhara.
You can pray for better proposal in your Du'a.
'Wassalam.