I tried to hold it in but couldn't I did 2 silent burps my teacher she stared at me I excused myself but after that I just kept burping it got loud and she gave me detention and it was embarrassing

We weren't there. Loud burps, contorting your body to get them out, laughing, etc, is one thing.
Next time say "I can't keep them in" or "They hurt if I try" and ask to go to the restroom.

Was this after lunch? Do you burp at home? Do any insides hurt when you burp?

I'd speak to your teacher after class tomorrow to find out why you were given detention. If you disrupted the class, and were laughing, I'd do the same thing.

Burps can be released silently very easily. I'm guessing that's NOT what you did. The is no excuse for a loud disruptive burp, excusing yourself does not get you out of it.

Yes it was the class after lunch I don't normally burp and I am never in trouble and don't disrupt classes so it was very embarrassing

Okay, so it happened. It's over, move on and stop dwelling on it.

Detention is already done, burping was already done, disrupting the class was already done, and you can't move backwards, so from now on, if you have to burp, do so quietly without disrupting the class.

Obviously your burping was noticeable, otherwise the teacher wouldn't have noticed. I have a feeling there's more to the story than just you burping in class, it's not hard to make a burp quiet and unnoticeable, so I'm pretty sure there was clowning around, and loud burping, that was disruptive. So you got what you deserved, and now you have to accept it, learn from it, and move on.