Hi Lara,
The original one I posted was purely just the blend tool.
Being as the 4 blends need a common touch point I created a temporary surface in this position to make the first blend.
You can then blend to the blends themselves diagonally after this.
The modified version I created a small gap so they where not touching also I modified your shape a little as it had a tight turn at far end.
Hope this helps.
Barry