In your early post you say that you used play sand.
Sand casting needs a sand mixture, a fine clay mixture and damp.
The correct consistency I squeeze a ball in my hand and then break it in half. If it breaks in two lumps it's fine .
Also in your drawing ,I would add another sprue as a breather from the top of your casting. Don't pore your metal too slow.You must also tamp the sand around the pattern.
WJF