$2000 is not the credit. $2000 is the maximum amount (for each person) that can be used to calculate the credit. Since you are eligible for the maximum 50%, $1000 is the credit your should be expecting ($2000 x 50% = $1000).
As Criiter-3 pointed out, if your spouse had also made a $2000 (or more) contribution, you would have then gotten a $2000 credit ($4000 x 50%).
You do not get to count any of your $4708 contribution in the spouse column on form 8880. She must have made her own retirement contribution.
