@OP
Your frame ain't bent, your wheel's badly dished.
You are able to centre it between the chainstays but not the seatstays because of the orientation of the dropouts. Ie, if you had long vertical dropouts you would be able to centre the wheel between the seatsays but not the chainstays.
Put the axle right to the back of the dropouts (remove the chain if necc) and it should be off centre at both seat and chainstays, give the appropriate side half a turn to start with and go from there to get it dished correctly.
*This all presumes that the hub is spaced correctly.
@OP
Your frame ain't bent, your wheel's badly dished.
You are able to centre it between the chainstays but not the seatstays because of the orientation of the dropouts. Ie, if you had long vertical dropouts you would be able to centre the wheel between the seatsays but not the chainstays.
Put the axle right to the back of the dropouts (remove the chain if necc) and it should be off centre at both seat and chainstays, give the appropriate side half a turn to start with and go from there to get it dished correctly.
*This all presumes that the hub is spaced correctly.