Formwork strip foundation garden wall

Hello community

I need your advice.
I started a project in my garden. A garden wall is to be built with formwork stones.
My original plan was:
Dig 90 cm deep, put in reinforcement bars. Then fill with concrete and subsequently set the formwork stones.
So far so good.
Then I rented an excavator and started digging.
Instead of the 30 cm width, I now have a 50 cm (+- 5-10 cm) wide trench.
I have a few options now.

1. Put in larger baskets and fill with more concrete. The entire garden will be filled up by 30 cm later.

2. Formwork with shuttering panels. Remove the panels again and sell them cheaply on eBay.

3. Permanent formwork with xps panels.

What do you think?
Or does anyone have a better execution?

I tend to option 2.
But I’m unsure.

Best regards

if you are already 90cm deep now and then add another 30cm of soil, you will be at 120cm. Do you want to rebuild the Great Wall of China. With such a generous strip foundation, you don’t need any steel.

if you are already 90cm deep now and then another 30cm of earth comes, you will be at 120cm. Do you want to rebuild the Great Wall of China?
With such a generous strip foundation, you don't need any steel.

The 30cm only applies to my garden.
There is a ditch at the back (but a very small one).
The structure should be as follows.
10cm gravel. 80cm concrete.
Formwork stones 170cm.

You can also simply use larger formwork blocks as a foundation.

You can also simply use larger shuttering blocks as a foundation.

I think that's a good idea. I would then also take 36.5 blocks. How would you then execute the first row?

I see various problems here now 1. Trench too wide -> either completely concrete it or fill it compactable on the side. In order to not get the trench rammer beside the concrete, you would then have to widen the trench further. 2. Trench not as deep as planned -> how frost-sensitive is your subsoil? 50cm is already not little, on many soils that is sufficient. 80cm is usually exaggerated. Or do you have another problem that is not clear to me right now?