What do you mean going everywhere in the corners? Is the tension set right on the blade? When I do corners I go into the corner, back out a little then cut the kerf about a blade and half size bigger in the waste make my turn go in the corner then cut again this gives me good 90 degree corners. Or once you go to your corner pull slightly to the back of the blade and in once swift motion as you are keeping slight pressure on back of blade make your turn. I would suggest making some practice cuts on a scrap, make some marks at 90 degree using a square and practice, once you get the hang of it its easy, I still like doing my first suggestion in cutting out the waste to make the kerf wider then turn and slide my blade into the corner.
If your blade is wondering your tension might be too loose, on my craftsman saw I like to to tension the blade as tight as I could without breaking it, on the excalibur I can't really make it tight it tensions with a flip of the lever so tension is perfect everytime.
