Health insurance - I turned 26 in 2018 and bought a Marketplace (Obamacare) plan; before that I was on my parents' insurance (I have a 1095-B). How can I file?

The only options seem to be private health insurance plan OR Marketplace (Obamacare) plan, but I had Blue Cross Blue Shield coverage through my mom's plan from January to April 2018 and then my Marketplace plan started in May. How do I select both so that I won't have to pay a penalty for not being covered (I was covered all year)?

(Please don't just say I can't enter 1095-B; I've already read that several times)