Translation:Excuse me, what is your name?
Technically, 叫 is a word for call. So if you asked "你叫什么?," the translation would be "What are you called" instead of "What is your name." If you wanted to ask "What is your name," you would use the word for name "名字." So, all together you could ask "请问，你叫什么名字?" or "请问, 你的名字是什么?"
You could argue that 你叫什么 is an abbreviation of 你叫什么名字, so the meaning it implied.
"Excuse Me" as a translation for 请问 is a bit iffy and really fails to capture the literal meaning of the characters. "Please may I ask" is a much better translation for all the other situations where 请问 might be used.
No, only when asking questions. In your situation, 对不起 would be acceptable.