One was probably laying the eggs and the other fertilizing them.
Because it is on the heater, you may want to unplug. But if they are all a white color they are bad anyway and won't make babies. You can get a breeding slate or get a slate rock from a landscape supply or rock yard.
You will likely want to have another tank/tub set up for them and ready for the next time. There will likely be a next time as you must have a pair.
Here is everything you might want to know about Angelfish and having/raising babies.