If you were going to damage the frame by twisting it under the load of its own weight, we all would be waiting in line at the frame shop!
My driveway is so steep, if you back out straight, you will slam the bumper into the pavement. If you back out at too steep of an angle, one wheel will be off the ground for about 1-2 feet of distance. If the frame could not take this much 'slight' twisting on a daily basis, I would have to junk every car I own after two or three impropper trips down the driveway.
Don't worry the frame is okay.
Get those tires checked soon.....
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles