You need to remove some links. That prong is way too big for now. Fitting it wrong you are more likely to injury the dog than if it is properly snug. Please read and follow that linked article!
EDIT-I see you posted. Don't buy a cheap collar; just remove links from the existing one. A collar with smaller links actually gives a harsher correction.
NAPWDA Certified Cadaver Dog
Waiting at the Bridge (italics
=GSDs) (hemangiosarcoma=blue):Grim , Cyra, Toby
, Rainbow, Linus, Oscar
, Arlo & Waggles