No.
Pokémon stats are calculated with a formula that takes into account several factors - base stats, IVs, EVs, level, and natures. Of these, only the base stats are modified by evolution (though likely the Pokémon also leveled up before it evolved); its effort values will remain unchanged and you can raise them in exactly the same way as before. It will have precisely the same stats at level 50 whether it evolved at level 50 or 10, so long as it gained the same effort points.
