The Rollei Classic 400 120 size film IS Agfapan 400 emulsion, but it is not coated on as thick a base as normal 120 film, rather it was cut from a master roll intended for 35mm film production.
There are several things you can do to minimize curling. 1. wind the film onto the developing reel in the reverse direction of the curl. That would be emulsion out, rather than in. 2. Don't over fix in hardening fixer, or try fixing in a non-hardening fixer, just be sure to keep your wash water close to 68f. 3. Hang film to dry with a weight at the bottom. 4. Sleeve your negatives in a page sleeve and put it under several heavy books for a few days.
Even with extremely curly film, I have been able to coax the strips into page sleeves. Once in the sleeves, under a few books for a few days, most film will flatten out. In worse case situation, I suppose you "could" dry the film on the reel, wound in opposite direction to curl..that is emulsion out.