I always put in some salt when I think there isn't enough, but then I end up putting in too much of it.
ご質問ありがとうございます。
"I always put in some salt"=「私はいつも塩を入れる」
"when I think there isn't enough,"=「(それが)十分ではないと思うときに」
"but then I end up putting in too much of it."=「でも、そうすると、結果的に私はそれを入れ過ぎてしまうんだよね。」
ご参考になると幸いです。