When making Tzitzit are there any rules regarding the garment itself? I am able to prepare the knots myself and have split a T-shirt along the sides where there was previously stitching, but only part of the way (about 2 inches) in order to show it is a four cornered garment. Could you tell me if this is correct or do I need to alter it?

In order for a garment with a slit up the sides to be obligated in Tztzit the slit should be longer than the closed part of the garment (Oruch Chaim 10;`7). A short slit is not sufficient. You should try to show the specific garment to a Rabbi to get instructions.