If you are having any symptoms that are concering (palpitations, shortness of breath, chest discomfort), you should be evaluated by a licensed physician who can complete a history and physical examination to assess your symptoms. This may or may not require additional testing such as blood work or an ECG. However, I agree with the others that you should not come to any conclusions without the assistance of a health care professional.
If you have not had a doctor check out your heart, you don't have enough information to be scared or not scared. Do yourself a favor and go in for a discussion of your symptoms and your fears.
Only then can you have some idea what's happening or what to do about it.
Most arrhythmias are benign in a structructally normal heart. It is a very common complaint. Most everyone experiences palpitations at one time or another. Your doctor will probaly do a 24hr monitor to see what's going on. They might order a echo to check on your structure. This is just a ultrasound of your heart. Your young so I'm sure all is well.