Fails to take GST Registration

Hello sir , I am small traders my total sale crossed 20 lac on 6.1.2018 but due to lack of knowledge still I have nt taken Gst Registration so I want to know that there is any penalty/late fees for not taking GST registration in stipulated time ? & also want to know whether late fees will b levied for late filing Return. I want to take Registration under Composition Sechme. thanks in Advance