Hello Stef.

  As the case and follower are of a plastic composite I would try applying a small amount of a silicone based lube to the inside of the magazine or a dry lube such as graphite and then work the follower repeatedly by hand using a piece of wood that closely matches the the dimensions of the follower to keep it level while working in the lube . I cant imagine you took any tension of of the spring steel follower spring . That is nearly impossible unless it is tempered with high heat . If that doesnt work there must be a burr somewhere in the magazines side walls or in the follower itself and would need to be polished out . If you take the magazine apart again you can always attempt to stretch the follower spring and increase the tension but you are on your own and may need to resolve yourself to the idea of having to replace the magazine should that fail . Good luck to you sir .