Just be patient, it will seal.
For me the biggest problem was sealing the top stave, where the bung hole is. It doesn't stay wet enough most of the time, so some canning or bees wax works great for that spot.
I recently let my barrels dry out completely, then wanted to use them again. Using a hose, I would let water pour in at full force, but it would leak out the bottom as fast as it went in. The barrel would never get more than about 10% filled.
However, I would spray the inside with water, place the bung in it, and let it set for half a day. Then I would repeat. After a few days of this, the staves started swelling again and now, these totally leaky barrels are again sealed just fine and filled with wine. Patience is the key.