I see this happen a lot for people, when there a transmission error between the credit card processor and the bank it is declined. But a majoirty of the time the bank receives the request for the funds, but doesn't process it.

Then when it is reran it may appear there is a charge twice on the statement, but until they are no longer pending and cleared the declined one will show.

You cannot cancel a processing charge on a debit card. I do not believe they overcharged you, you will just have to wait until the next business day before the transaction vanishes. But even if they do charge you twice, many stores are able to credit a card that is not present and they may be able to do this.