On top

Sooooo. I don't know how to be on top, is that bad? I've done it once and I thought it was terrible. Not the sex part but me. I just felt like I wasn't doing right. Not even sure there is a 'correct' way but it was just a feeling. My  boyfriend at the time kept asking and asking, "be on top. Be on top, please?" But after the first time I just refused to do it. Now my current boyfriend doesn't know that cause he hasn't tired to make me be on top. Will someone please explain to me what is wrong?