Open the Wallet App, tap on the + icon at the top and then look in the "Cards Found for You" and the "Cards from Other Apps" sections there and see if the card you removed is there.
Also, are you sure you removed it? What exactly did you do? Maybe you just moved it behind the other cards.
Removing cards requires several steps and confirmation of removal. It can't be done by a single action or swipe.
If you did, you, may need to wait a couple of days for your bank or card issuer to process the removal, before you can add it again.
Also, go into your cards app and se if you can re-add it from there.