Not enough blade tension could be one reason why your blade is wandering, you have to consider saw speed as well, generally when cutting thin material you should slow your speed down. I would suggest you practice on 3/4" pine first, cutting out simple shapes such as hearts or circles. Dont get hung up on staying on the line. Depending on the pattern, it may not matter, and the only one who will know is you. It's a great hobby, stick with it.