What do i do if my blue elastic spacer popped but it's still in there it did not fall out. Is it still good ?

You should be just fine, until your visit. The visit should be in 1-2 weeks.  Be sure the orthodontist or the technician knows it is in there and removes it at the appointment.  It will still function as long as it is in between the teeth.Dr. Greg Greenberg

Yes, it is still good. Spacers usually will be left in place for about 1- 2 weeks before they are removed for the procedure planned at your next appointment. If they are left longer than 1-2 weeks they may pop or just fall off as small spaces are created where the spacers are.