Twelve inches is ideal, but that doesn’t mean you will not have success with a LOT of vegetables. Did you break up and loosen the soil under? Remember plant roots will take advantage of that, too! Even if you have not you, you can do that if you haven’t yet filled the bed with soil. Here’s our general advice, which addresses these and other aspects: https://www.almanac.com/content/how-build-raised-garden-bed
Twelve inches is ideal, but that doesn’t mean you will not have success with a LOT of vegetables. Did you break up and loosen the soil under? Remember plant roots will take advantage of that, too! Even if you have not you, you can do that if you haven’t yet filled the bed with soil. Here’s our general advice, which addresses these and other aspects: https://www.almanac.com/content/how-build-raised-garden-bed
We hope you harvest a heap!