Why not set ping limit to 500, if you know that your ping is above 300?
So you think, only because you created room, ping limit shouldn't affect you?
If it's only you then problem obviously is on your side. Maybe talk with your ISP.
And what intranet connection you have? You sure that nobody else is using internet while you are playing?
If someone is downloading something, or watching movies online, then it can affect your ping (but it depends from internet speeds up/down).