Your brand new Gi is a tad too big?
You may try these steps to shrink down your Gi to fit you:
1. Wash your Gi in cold water
2. Tumble dry it in a heated dryer until completely dry for maximum shrinkage (shorter time for a lesser shrinkage)
NOTE: Different weaves and fabrics will shrink at different rates. What worked for one Gi might not work the same for another. Your jacket and pants may shrink differently too! Do try to get the closest fit whenever buying your Gi by checking out the brand's Gi size charts or inquire before purchase.
DISCLAIMER: Consistent drying your Gi in hot dryers may weaken the material and/or cause the colour to fade prematurely