Hello @carmenrubio1,
Like in real life, you can’t inflate an object that is not a volume!
Imagine a cushion! Even if flat and not inflated, it has the potential to be, because it’s more or less airtight, has a sealable intake of sorts, and at least two sides that are sown, glued, or fused together, forming the pneu. All these parameters must also be met to simulate this, except the intake, which doesn’t even have to exist.
Now, could you be a little more precise on how you want the end result to look? What shape are you after? Do you want a single air chamber or a couple? If you want the air structure to stand like this, without supports, you probably need to be very peculiar about the design.
Your current geometry, when inflated, would probably look like a slightly bend salami.