Hello,
I would caution you to confirm that you have the correct tank. The filler necks are different on different model tanks, and can cause exactly the problem you are experiencing. They are not a lot different, but different enough not to fit. If yours is your original tank reconditioned, then probably not the problem (unless the filler neck got bent in the process). If yours is a different/replacement tank - compare the filler neck angle, bends, and length with the original. I encountered exactly the problem fitting the used replacement tank I bought to my 230SL - just impossible..... probably a 250 or 280 tank. When I returned that and got a new correct tank, it just slid right in.
Granted there are slight obstacles you have to navigate around. If you have the neck of the filler bearing against the side of the body hole for the filler, and the hole for the stud still isn't correctly located, something is amiss (and it probably isn't you).
Regards -- Roger