Could someone answer this question about my taxes?

i did my taxes with my boyfriend we live with each other and we have a 2 year old baby were not married and the lady that did our taxes marked the box that says (married filling jointly even if only one had income) was she suppose to that? was i even able to do my taxes with my boyfriend? am just worried because my moms worried she doesn't want me to end up owing money to the I.R.S.