Since Sheridan took the reigns at Home Park, the Pilgrims have lost just once in five games.
But the Plymouth boss, whose side now lie outside the relegation places on goal difference, insists his side's displays have not been good enough.
Sheridan told the club's website: "Performance-wise we can play a lot better and I expect us to play a lot better.
"There are eight teams who are going to be fighting and it will go right to the wire.
"We've just got to concentrate on ourselves and if we can get one or two victories early on it should get us in a better position."