Gamo Hunter Sport pellet gun upgrades?

Okay, by recommendation by people, I have added a GRT III trigger to my Gamo hunter sport, and also bought a BSA Optics 3-9x40mm Huntsman Scope. I shot it a bit today, and I can't get a good spread. why is this? do I need anything else? This is really disappointing. and I am not looking to buy a new gun yet.