Hi,
whatever money you have received from your parents is accounted as gift received from blood relations and it is tax free, you can show this amount under exempt income whiling filing returned.
as far as question of penalty concerned while filing last year IT return, it depends if there was any taxable income on which no tax had been paid. if you had paid all the tax and no tax was due, and you just havent filed the return,
then there will be no penalty.
as you haven,t filed any returns and you have deposited Rs 3 Lakhs in your bank account. you May received notice from IT department to disclose the source of income of Rs 3 Lakhs.
you may refer this link regarding penalty and filing of IT return.
http://taxguru.in/income-tax/converting-black-money-white-declaration-scheme-proposed.html.
you can file return for FY2015-16 upto 31st march 2017., it is better then never