Can I return bought goods to charity shop?

You may have a consumer protection act where you live. Does it apply to your case? You would have to check it out. The problem is that you sought the benefit of a bargain. It failed. A really important example was the case of people selling their money for 2 percent of face value as the fled from WWII Europe. Some tried to get a portion of their money back. That effort failed. You might consider how what is best for you for other than money reasons.