Name troubles.

So, anyway, for those who don't know, I was born waay before my mum and dad married. So long before, that I don't actually know if my dad is my dad, or my older brother's dad is my dad. [[srsly. I mean, why else would my mother let me go visit him when I was younger]]
This means that my name isn't the one that they tell people. Instead of being the one that my mother signed me up with school for, it's actually something completely different, first name and all.
Why is this a problem? you may be wondering. Well, for those who don't know, this year in school, we start GCSEs, which are hugely important tests that English students have to sit, which take up most of the last three years of high school. In these tests, you have to have your correct name on the certificate. How do I know this? Well, today in form, our teacher told us to ask our parents if our names were correct, and if they were not, we'd have to go to her and tell her what they actually were.
That, my friends, is the problem.
You see, for all the years I've been at my high school, everyone's known me as Ruth *insertsurname*. [[most people know my name anyway; not that bothered about creepers.]] That was it; no secret agendas, no whoremones, nothing. And now I have to delve through my history, and drag up my birth certificate which has my real name on it, which I did yesterday, and I found out that I wasn't Ruth; I was actually a completely different name.
Of course, I knew this already. But now, I have to tell my form teacher, and then everyone in my class, about my complicated family, and how I've lied to them for all these years.
Or do I?
What should I do - go through life with qualifications under a fake name?
Or admit that I've lied and that I was born out of wedlock?