Is this correct?
I thought how (much) immature I am.

There was asmall happening or an small accident that made me feel how (much) immature I am.

Question

Is this correct?
I thought how (much) immature I am.

There was asmall happening or an small accident that made me feel how (much) immature I am.

Answer

I thought how immature I am; though strictly speaking, you should write "I thought how immature I was", as this is an occasion of reported speech (or thought in this case). It would be correct to write: I thought “how immature I am”, using the inverted commas as shown.

Answer

It would be correct without the word "much", and if you wrote "a small".