H2(g) + Cl2(g) → 2HCl(g)
Molar ratio of H2 to Cl2 is 1:1, so hydrogen is in excess. Molar ratio of H2 to Cl2 to HCl is 1:1:2, so 2 litres of HCl will be produced.
So in total, after the reaction has occured, you'd have 2 litres of HCl + 1 litre of excess H2 = 5 litres of gas.