4 weeks @ 300mg isn't too bad. You should see the water weight drop pretty quickly.
I have to question the wisdom of your decision though. Being your first cycle, you could gain some lean mass as well as water weight as you have experienced. The scale weight only tells part of the story. Scale weight combined with BF % is more telling. Also, personally, I find it harder to diet on test. Test makes me hungry. The only reason I cut on test is to be able to hang on to more muscle and for me, I find that there is no difference at 200mg/week or 500mg/week in that regard so I opt for the lower.
If you were monitoring your BF % you could have a better handle on your progress regardless of water weight or lean mass gain.