collocation

[Poshi]

Hi,
Can I ask about a collocation of words, please?
I wonder if I can use "get across" and "what I said"?
like this: I couldn't get across what I said.

I also want to ask about "make ... understood" and "my idea / thoughts / message"
Can I say like this?: "I couldn't make my idea understood."

[sandhya.sha]

Hi,
Can I ask about a collocation of words, please?
I wonder if I can use "get across" and "what I said"?
like this: I couldn't get across what I said.

I also want to ask about "make ... understood" and "my idea / thoughts / message"
Can I say like this?: "I couldn't make my idea understood."

In the first sentence, when you say "I couldn't get across what I said", it means you didn't understand what you said. What you meant was you couldn't make someone else get the meaning of what you said. In order to convey that meaning , rewrite like this:
"I couldn't make them get across what I said."

As for the second sentence, yes, you can say "I couldn't make my idea understood"