I made a account on Wbaduk a long time ago but never played there because I was too weak.
In the last few days I started to play on Wbaduk now and since my rating was set to 25k I thought I could play around until I get to my actual rating which I thoght was around 15k. In the first game my opponent was a total beginner and I felt bad at defeating him.
But the next few games were totally different the players were so strong! I barely won against some and was even totally crushed with a point difference of 150+.

I read here that there are many sandaggers, so I wanted to improve my rating to get away from the sandbag rank and therefore I continued to play.

I post this game since it was really fun. I made many mistakes and my opponent punished even really small (I think) mistakes, he was really strong. I also found some weaknesses and sometimes it worked well.

Well here is the game, questions are as comments in the game
I was black and lost by 72.5 points



After that game I was asking myself:"Did I get weaker?" and so I played 1 game on KGS against a 6k with a 4 stone handicap, The result was amazing: I won by resingnation on the 53th move.

My question is:
Is playing against stronger player (sandbagers in this case) improving my fighting?

To improve at fighting, fighting itself is necessary but not sufficient.
You also need to:
(1) improve all your basics (basic shapes, basic tesujis, basic life-and-death, basic strategies);
(2) know when and where to start a fight and when and where to avoid a fight.
(A good teacher can help you.) A few ideas:

Thank you EdLee!
I really have to take care of my bad habits, this could be very difficult.
I guess I should slow a bit more down and try to stop me when I think about a bad move.

Looks like it I still have a very long way to go