I have a Sig Rascal 40 running a Thunder Tiger 46 Pro 2-stroke engine. The plane has always been kinda squirrely on take off...doesn't track very straight at all. Anyone else have this problem?

As light as the plane is, and with its long tail moment, it will weathervane very easily if you're taking off in a crosswind, plus it does what all tail draggers do when you hit the throttle--turn left if you don't counter with right rudder. It's probably the most difficult plane I have to keep straight on take-off; I practice with it for that reason.
You might want to play with the landing gear and bend the axles to toe in the wheels a little; just enough to notice they're not parallel, a couple of degrees. Toe -in makes the plane want to self correct its straight ahead roll.

Another thing perhaps worth trying: take the undercart off and reinstall it back to front so the wheels are a little closer to C of G. It may not look quite right but may improve ground handling.

Mine's not too bad on the ground (grass), but on the odd occasion, I have got into a bit of an overcorrection cycle with it on take off than can look kinda messy.