How do you prove crossover between parents' health insurance and coverage under a plan through Obamacare? 1095A obviously does not show coverage under parents' plan.

I was covered from Jan-April in 2018 under my parents' health insurance. In May (my 30 day grace period), I enrolled in a plan via Obamacare under special enrollment starting June 1. As a result, my 1095A only shows coverage from June-December of 2018, and I don't know how to prove I was covered under my parents' plan until that time (with the exception of one month only - May). Turbotax now says that I need to pay the penalties for not having insurance, when I was covered until purchasing my own plan. Please help!