Hi mala.. This a member to member Board and must communicate directly with seller to resolve issues. I assume the seller has corrected by refunding or replacement.
Buyers cannot alter their feedback. Seller can request a revision that you would agree and change..
http://pages.ebay.ca/help/feedback/revision-request.html
Message seller and let them know that you are willing to amend if a request is filed.
Feedback should be left only after a transaction is over with all issues resolved. 60 days to leave.
Buyer Protection is available for items not received and not as described..
http://pages.ebay.ca/help/buy/paypal-buyer-protection.html
File , if necessary, within 45 days.