See, we were the opposite. Colton never wore newborn and was out of 0-3 month stuff when he was 1 month old. Right now he is in 12-18 month clothes and has been since he was 10 months old.
If you end up with a bigger baby it would be the same. (Colton was 9lbs14) So I would suggest not stocking up on anything right now. For many reasons: 1. You dont know what size your baby will be; 2. Depending on their size (smaller, average, bigger) they will be in a different size during the colder months and if you bought say all 6-9 months in winter clothes, then you end up with a big baby who weres 6-9 while it's still warm all your 'colder' clothes will have been a waste. (if that makes sense).
I would suggest putting the money back for clothes, but not going overboard right now. Plus, you will have alot of clothes given to you as well!