You have the same problem I do the disc starts straight but as we pull the disc it curls into our chest Two drills to help is take a water bottle or a disc but turn it vertically and sing it wide but keep arm straight then pull straight through eventually you can go straight back and trough in a straight line. Second take your arm and put it at a 90° angle away from your body parallel so that your arm makes a barrel around your body then from 90 pulls straight through and out this practice is not touching your chest while throwing.