I'd be pretty mediocre at disc golf if I could putt....
But I'll throw out one suggestion anyway . . .
Grabbing a stack of putters and tossing putt after putt is different than when you are playing a round. When you are practicing, you can adjust your next putt based on the last one.
In contrast, during a round (especially a tournament round) you may have long intervals between putts. Consequently, you don't get the chance to immediately correct off your previous mistakes.
One thing that helps me is to practice upshots and then putt out from wherever the upshots land. I find this a better simulation of actual play versus just putting a stack of putters.
If you don't have the room to throw upshots, try tossing putters to random locations around the basket and putt them out.
Good luck!