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.
