Im 25, had open heart surgery at 4 and my ekgs have abnormal t waves. 3+ doctors heard an arrhythmia and said not to worry. what should i do about it?

Don't worry about it: You have by your own account over 3 doctors tell you not to worry about it. They have the advantage of knowing why you had surgery and what was done. Plus they can examine you & look at your heart with an echo etc. A t wave abnormality is fairly non specific. Same can be said for arrhythmias. Your doctors can take that info and apply it to the proper context. At some point you have to trust them.

See a specialist: It truly may be that your condition is not concerning. However, typically an arrhythmia cannot be completely assessed by listening alone. There are a number of late problems that develop in adults that were treated for congenital heart disease. There are now physicians who specialize in the care of adults with congenital heart disease. They are best equipped to provide a comprehensive evaluation.