You get the bottom slot filled first. Took me a while to get it, i missed that there was another valid move for the second push. The only valid first move is to move the right block down. The correct next step is to move the left block, not the right block a second time.
**SPOILER SOLUTION**:
with block1 being the left block and block2 being the right block
block2 down - block1 right - block2 right - block1 down
then it should be pretty straightforward