I'm baffled as to why Honda chose to design the front sprocket mounting system the way they did. Many machines I've owned had side to side play and of course some front to black play also. I had Zuki's with the same problem.
Not sure why the countershaft isn't threaded and the shaft machined with a shoulder in which to tighten the sprocket against. I forget who else uses that type of mounting but it might be Yamaha and others. Honda's 4strokes use the shaft and sprocket splines alone to hold it on there. 250R gets the solid mounting.
On some Hondas, that mounting allows the front sprocket to float a bit. Maybe there is less drag???? Why did 4 strokes get the sloppy mounts (ATC and XR/XL's) and the 250R got the spline and shoulder mounted type?? 4 strokes have lots of torque, 2 strokes have wheel spin - why would the fastenening change??
Anyhow, I've had some fairly loose sprockets. The shaft is hard and the sprocket is softer. Your new sprocket may tighten it up alot, but don't worry too much if it's still sloppy. When it starts getting deep notches, then you can worry.
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country