Welcome to the forums!
The answer to question 2 has to do with counting. At 19k, you may not think you’re at a point when counting matters during your games. But it mattered here because the score was so close. I assume you know how to count territories, but maybe you don’t know how to count move values yet. To count a move value, you need to compare the value of playing there with the value of your opponent playing there.
Take my variations for your C4 move. Variation 1 is you playing there, and variation 2 is your opponent playing there. The difference is 1 point, because Black lost 1 point and White gained 0. So, following this process, you can see that C4 had some value, but the value was small—only 1 point.
Now take my variations for J8. Variation 3 is you playing there, and variation 4 is your opponent playing there. The difference is 3 points, because Black lost 1 point and White gained 2 points. As a result, J8 was 2 points better than C4. And it so happens that Black’s lead was fewer than 2 points.
I suppose that answers question 1 as well, because the 99% win rate might make you think you were winning by a lot when it just wasn’t true.
By the way, 3-3 on move 3 is rarely good. Try one of the 3-5 points. Any will do.