A 92% Polyester and 8% Lycra (brand name for Elastane) mix has the ability to return to its original length, shape, or size immediately after the removal of stress.
Anecdotal sources suggest that it will eventually 'stretch out through washing and wearing'. Washing on high heat for at least one full 35-minute cycle can stretch your fabric a tiny bit.
As per eHow, you can put the garment on while it's still wet and wear it around the house. Allowing it to dry on your body may help it form to your body, thus stretching it out just enough to fit.
If the fabric stretched out enough, then continue washing it under high heat and allowing it to air dry.
Another method is to 'stretch it out on a flat surface'.
• Start by washing your fabric in a high heat cycle for at least 35 minutes. Remove the fabric while it is still hot, then place it on a flat surface.
• Secure one side of the fabric with something heavy, like a free weight or a few heavy books. Stretch the fabric as much as possible without tearing it. Secure the other side of your fabric with another heavy item.
• Allow fabric to dry. Let it sit for an hour after it's dry. Remove the weight from the fabric and see if it is stretched to your liking. If not, repeat the process.
Learn how to shop for a flattering wardrobe and what a tailor can do to help at Womansday.com.