回答
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I can't quit now because that would be a waste of the time I have put in.
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If I were to quit now that would be a big waste of my time and effort.
1) I can't quit now because that would be a waste of the time I have put in.
「今までにつぎ込んだ時間が無駄になるから辞められない。」
the time I have put in で「私が今までにつぎ込んだ時間」
2) If I were to quit now that would be a big waste of my time and effort.
「今辞めたら、時間と労力の無駄になる。」
my time and effort で「私の時間と努力」
「無駄」は waste と言います。
ご参考になれば幸いです！
回答
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If I quit now, it would only make all the effort I put in so far pointless.
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If I stopped now, all of my hard work would go to waste.
今までの経験 = hard work so far / effort up until now
無駄になる = to be a waste / to go to waste / to make pointless / to make useless
から = because, so
辞めれない = can't quit/stop/give up
この翻訳したものは全て例文に使えます。
例えば:
If I gave up now it would make all of the effort I put in so far useless.
「Because」や「so」の代わりに「if」と「would」を使いました。それはもっと自然の方です。
日本 
アメリカ合衆国 
