Is Audit mandatory if i am ready to pay 15% of my gain

I am salaried person having annual salary of 4 lakhs. A
long with it i do trading my trading details fr (FY17-FY18) is as below (taken from zerodha Tax P& L)

INTRADAY GROSS PROFIT: 936.70
INTRADAY TURNOVER: 1,708.90
SHORT TERM GROSS PROFIT: 15,595.05
SHORT TERM TURNOVER: 3,42,266.30

1)is Audit is mandatory for me ?
2)how to pay tax for my gains ?
3) which ITR form should i use ?

kindly clarify these queries

Thanks

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