You're probably going to be fine.
However, as this is obviously troubling you perhaps you should tell your parents and ask them to take you to the doctor for a check up.
Your doctor should ask you about family history (to see if there has been anyone with sudden death or heart troubles in the family) and should check what medications you take.
The doctor can arrange an ECG (or EKG if you are in the USA) and if necessary a Holter monitor
The symptom you are having is called Palpitations. It is unlikely to be related to a heart murmur
and is not a heart murmur itself.