Dear Sir

I am working as a Accountant in Restaurant. I have filed GSTR-3B .But not filed GSTR-1.Because GSTR-1 has a time extended up to 30-1-2019. Our restaurant Turnover more than 1.5 Cr. Per Ann-um.  AtPresent. Up to Nov-2018 GST Returns filed by consultant. He filed Return whatever data given by me he filed Return with same. We are 5% GST  charged on Sales, that same pay tax and filed return without claim ITC.
But Dec-2018. Return filed my self. In this Dec-2018 Return I claimed ITC Rs.10,200/-.against officially appeared in more than Rs12,000/- in GSTR-3B. and deduct that amount remaining amount pay tax (Total Tax Rs.1,36,668 - Rs.10,200= Rs.1,26428 Tax paid) Return status is submitted not filed.
Consultant feel angry and told to me that you are wrongly filed.you are claimed Rs.10200/- ITC in Dec-2018 GSTR-3B.  So tax rate changed from 5% to 12%
I have under the following doubts.  
1. without filing of GSTR-1  we can file GSTR-3B first
2. According to Consultant If ITC claim in  GSTR-3B Tax rate may change 5% to 12%
3. If wrongly file return  How can I to rectify it 
4.Any  penalties or notice would be come from department

Thanks & regards
Rama Mohana Rao Pilla