I am engaged to be married and I really like my fiancé, but I have been out with 2 other guys (before I became engaged). We didn't get up to much I am still a virgin. Should I tell my fiancé about this knowing that if he finds out he will call the wedding off? Or should I keep quite?

Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
No doubt that what you practised is a major sin and a clear violation of the boundaries set by Allah. Therefore, you must turn towards Allah making sincere repentance, asking His forgiveness and multiplying your good deeds. Perhaps Allah will accept your repentance and erase your sins.
Moreover, you should cover yourself as Allah has covered you. Do not inform anyone about your bad practice even your fiancé. The Prophet said: "Everyone who has been afflicted with some filthy acts should cover himself as long as Allah screens him". [al-Hakim]
Know that your fiancé remains totally an alien man to you as long as the marriage contract is not established. Therefore, you should deal with him as an alien man.
Allah knows best.