Parents of three or people that grew up as one of three children

Hey all! I’m looking for input as to what it’s like to either grow up as one of three kids or be raising three kids!

I only ever wanted two, but since my last was born I have this little itch to have one more. I’m totally torn and am worried that with three one will always be left out or third wheeled. I grew up with only one other sibling but she and I don’t get along AT ALL, and sometimes wish there were three of us so I could have a sibling relationship with at least someone. So that being said I have no idea what it’s like to be in a family with two other siblings. My biggest concern is the third whee thing because a friend of mine who has two siblings said that’s how it was growing up, someone was always left out. So please shed some light on it for me?