Water crystallization is a different effect and not relevant here. It has the same mass so it doesn't effect sea levels when it's frozen and it's not a linear effect, it won't continue to shrink as it warms.
But like everything else (to various extents) it will expand when it's warmer.
The maximum density of water is at 4 degrees. If you heat it above that it starts expanding quickly. If you freeze it below that it starts expanding slowly.
But like everything else (to various extents) it will expand when it's warmer.