I thought about doing it but then I changed my mind.
I quit before I even started because I changed my mind.
Changed my mind: gives the implication that you no longer want to do whatever it was you first thought about doing. The listener would understand that you didn't even begin with the task because you changed your mind.
I quit before I even started: means that you didn't even begin with the task at all.
Hope this helps!
Changed my mind（考えが変わった）:
「（やろうと思ったけど）やめた」という意味合いです。その仕事に手を付けなかったことを表します。
I quit before I even started（始める前にやめた）:
仕事に手を付けなかったという意味です。
参考になるといいです！
Both of these answers are an expansion on "I was going to do it but I quit".
You tell someone that you started to do a task or job, or whatever it is you are working on, but then you did not finish the task and left it without finishing. To be more specific if you were talking about a film you were watching you could say "I started watching the film but didn't watch the whole thing."
二例とも、「やるつもりだったけどやめた」を表す言い方です。仕事などを始めたけども終わらせる前にやめたことを伝えます。より具体的に、例えば映画を見ていたなら：
"I started watching the film but didn't watch the whole thing."
（映画を見たけど、全部は見なかった）
I didn't go through with it. - This means that although you were thinking of doing something, you did not do it.
I changed my mind and didn't do it. - To change your mind means that you were going to do something and then decided not to do it or vice versa.
-I was going to go to the party but then I decided not to.
-I wasn't planning on going to the party but then I changed my mind. I'm glad I did, I had so much fun!
I didn't go through with it.
それをやり終えなかった。
これは、何かをやろうと考えていたけれど、やらなかったという意味です。
I changed my mind and didn't do it.
気が変わって、やらなかった。
To change your mindとは、何かをやろうとしていたが、やらないことに決めたという意味で、その逆もです。
-I was going to go to the party but then I decided not to.
パーティーに行くつもりだったけど、行かないことにした。
-I wasn't planning on going to the party but then I changed my mind. I'm glad I did, I had so much fun!
パーティーに行く予定ではなかったけど、気が変わった。行ってよかった。とても楽しかった！
I started with good intentions but threw in the towel
If you start something 'with good intentions' it means that you originally intended to complete something. If you 'throw in the towel' it means that you give up or stop doing something (which has been too great a challenge).
何かを"with good intentions"（善意を持って）始めるということは、最初は達成するつもりだったということです。もし"throw in the towel"（タオルを投げ入れる）したら、（ハードルが高過ぎて）途中であきらめる、または、辞めるという意味です。
Partway through I realized I did not want to do this anymore
Three common and simple ways of describing that you wanted to do something or started and then decided to quit.
"Midway" used to describe something about halfway through.
"dedicated" is used when describing something you enjoy doing and have passion for, so not being dedicated is describing not having the passion or will to pursue the certain 'thing'
"partway" used to describe a snippet or part of the journey while pursuing something
何かを始めて途中で辞めたことを伝えるシンプルで一般的な三つの言い方です。
"Midway" は「途中で」という意味です。
"Dedicated" は、自分が好きで情熱を注いでいるものを表すときに使われます。ですから、"Not being dedicated" はそれを追い求める情熱や意志がなかったことを表します。
"partway" は、何かを追い求めるプロセスの一部分を表します。
I was going to do it but I only got partway through
I stopped before I completed doing it
If you do something to the end then you are said to have 'completed' it. if you only manage to do some of something and not all then you can say you got 'partway' through
物事を最後まで行うことは 'to complete' で表せます。
何かを途中までしかできなかったなら、それは 'I only got partway through'（途中でやめた）と表せます。
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