It's not uncommon for cotton clothing to shrink over time, especially if a garment accidently ends up in the dryer. Luckily, it's quite easy to stretch cotton back to its original shape and size.
Fill a sink or bucket with warm water, and add 1 tablespoon of baby shampoo or hair conditioner.
Completely immerse the article of clothing in the water. Allow it to soak for about five minutes to relax the fibres.
Remove the garment from the water and gently wring it out to remove excess liquid.
Lay the damp article of clothing on a flat surface, such as a table. Smooth the fabric so that it is completely wrinkle-free.
Pull gently at the garment in the direction(s) you would like it to stretch. If it needs to be stretched significantly, you can also use an iron on a low to medium setting to push the fabric in the direction(s) you would like it to stretch.
Place heavy objects (such as paper weights or canned goods) on the edges of the stretched article of clothing to keep it in position as it dries.
To prevent your garment from shrinking back to its original size, continue to wash it by hand and lay it flat to dry. If your garment does shrink again, you can simply repeat the stretching process.
Do not use an iron on any graphics or beading. Do not hang your garment on a hanger when wet or damp, as this may cause it to stretch out of shape.