not spherical enough

Hey guys. im doing my first dorodango and im having trouble shaping it into a perfect sphere. its quite round but far from perfect. which is what all the videos seem to portrait. right now the diameter of the ball is about 7cm long and im shapin it mostly with a 5cm diameter long shot glass. is this the reason im not able to get the perfect sphere. any tips on that or should i just try to find a bigger glass :(