Temp overshoot. Stat not switching off boiler

Hi folks. So I have two zones controlled by two wired stats. No TRVs yet. As I sit here now I have this zone set in the schedule to 20 degrees but the room is now showing 2.6 on the app and wired stat. The problem is although temp has been reached the boiler is still going and pump still firing.
Shouldn't the stat stop the boiler and circulating pump right when my desired set temp is reached ?. This is a constant problem and it's definitely wasting fuel.