The thing about these new-fangled ECG machines which analyse the trace for you is that occasionally they are right. Often, though, they are wrong.
Step one is not to worry. Step two is to get the ECG interpreted by a human being. If you're a healthy young person, it is unlikely that an ECG will detect an abnormality which will mean you can't get a Class 1. The two most likely possibilities to disqualify you in this way, which I would guess are Wolff-Parkinson-White Syndrome and Long QT Syndrome, do not show ST elevation on the ECG.
In any case, it is highly unlikely that you would have had acute pericarditis without knowing it.
QDM