ball joint popped off what to do now?? bmw e36?

[elm3rom3ro]

hello i installed new control arms in my e36 and after i finished one of the outer ball joints popped of so i put it back in than i took it to get an alignment after driving around i checked the car again and it was off again so i went home very slowly and when i got there i checked again and it was back in so what is going on here ??

what should i do?

should i let sit for a day or 2 to see if it will hold up or what??

thanks.