Insurance for me and my wife

so if i go thru the the insurance marketplace/ exchange for CT, if i get insurance individually it will be $203 and $248 a piece per month. but if we go together on a plan it will cost $510 a month which is a lot more a month. so we obviously want to go the cheaper route.

when signing up i have to put in either married filling separately or married filing jointly. if i do jointly i have to go for the more expensive plan $510 a month. but if i put separately we can buy individually and get the cheaper version of $203 and $248 a month.

my main question is if i put them both as filing separately and pay the cheaper amount will there be any tax penalties / fines for when i do my taxes as filling jointly? if i chose to pay the lesser and put filling separately? thanks!