Problem Distinguishing 〜つもり and 〜ようとする

Question

Ａ「お宅のこうちゃん、薬飲まないの？」
Ｂ「そうなの。あの子、（　　　）、いやがって口を開けないのよ。」
１　飲むことにしても　　２　飲むつもりでも
３　飲ませたつもりでも　４　飲ませようとしても

I chose ３　飲ませたつもりでも. The correct answer is ４　飲ませようとしても. I think

Ｂ「そうなの。あの子、（飲ませたつもりでも）、いやがって口を開けないのよ。」

means "I planned to make him drink it, but he hates it, and I can't open his mouth.", while

Ｂ「そうなの。あの子、（飲ませようとしても）、いやがって口を開けないのよ。」

means "I try to make him drink it, but he hates it, and I can't open his mouth." In English, these both sound fine to me, so I don't understand why ３　飲ませたつもりでも is wrong.

I realized maybe the reason is Ａ is using the present tense, 薬飲まないの？, so using the past tense, 飲ませたつもりでも, is wrong. Is that why?

Answer 1

～～たつもり(だ) means "I think I did~~".

飲ませるつもりだ "I intend / am planning to make him drink"
飲ませたつもりだ "I think/believe I (have) made him drink"

So 「あの子、飲ませたつもりでも、いやがって口を開けないのよ。」 would mean "Even though I think I (have) made him take/drink (the medicine), he wouldn't open his mouth", which would make little sense.