Can I get my watch fixed? The front glass popped off

It's unlikely your watch is still within its one year manufacturer warranty. When the screen pops off an Apple Watch, it's most often because the battery is old, has swelled, which pushed the watch face off and the watch cannot be fixed. It has to be replaced. You can see the cost of what is called an Out of Warranty replacement watch, but depending on the model watch you own, it may not be wise investment. If it's a pretty old or out of date watch, it would make more sense to just buy a new watch as opposed to paying the price for a replacement watch.

See this link for Out of Warranty prices --> watch Service Pricing - Apple Support

No, you cannot get it fixed for free if it’s out of warranty.