First of all, relax and don't overthink.
Now coming to your question, Yes it's normal to feel the metallic taste and smell in your mouth. It is probably due to the temporary filling, as you said you are undergoing RCT.
If the filling is dislodged from its place, just spit it out. But if by any chance you swallow it, no need to worry just drink plenty of water.
And don't be worried about the filling mixing with saliva, as the filling hardens after a few hours after its placement.
Next Steps
If you still feel worried, visit your dentist to get your filling changed/ look into the matter.
Health Tips
Start warm saline rinses two to three times a day, it may help.