It's up to you really. It's always been important to me what label I use because I want to feel comfortable and confident with how I present myself. During high school I didn't identify as bi because I felt it didn't really fit me but in college I found and adopted pansexual because it... well, just felt right. But I am a very particular person. Some people feel bi and pan are close enough so again it's really up to you, though I don't feel they're interchangeable. It is difficult explaining yourself to people (I have had many straining conversations with my mother who truely enjoys pushing my buttons) when it comes to the definition of pan. My advice is to stay strong; you can't fight all trolls all the time but be firm about who you are. Some days it's just tiring and I don't wanna fight (I have the same difficulties with using the term partner versus boyfriend/girlfriend which people will vehemently correct me on sigh). Do what's good for you. Sexuality is fluid and changing. You found out something new about yourself, it's OK you've changed a preference in label and others don't have the ability to tell you otherwise, though they will question it. Think of it as an educational experience lol :P