Baranwal is sub community of Bania,
So you can't have 'Bania' or 'Barnwal' as surname.
Pick any Gotra (Surname) of Baranwal.
There are 36 gotras in Barnwals. These are Garg, Vatsil, Goyal, Gohil, Kraw, Deval, Kashyap, Vats, Atri, Vamdev, Kapil, Galb, Sinhal, Aaranya, Kashil, Upmanyu, Yaimini, Parashar, Kaushik, Maunas, Katyaapan, Kaundilyam, Pulishh, Bhrigu, Sarvay, Angira, Krishnabhi, Udhhalak, Aashvalayan, Bhardwaj, Sankrit, Mudgal, Yamadgri, Chyevan, Vedpramiti and Sanskrittayan.
https://en.m.wikipedia.org/wiki/Barnwal