I thought that might be the case.. It's why I asked you for the conversion factors.
Nice job to work out the numbers as you did. You clearly see the problem now. This is a basic issue when doing conversions in SAP, (or any system for that matter). QM calculations are always done in the base UOM. (in your case sheets).
I believe that most consultants would recommend that the BUOM be the SMALLEST UOM that is used for the material. This isn't always possible either with certain materials.
If you do a search you'll find quite a few postings on conversion issues. TONS to GRAMS is one for instance. Even KG to LBS and back has been an issue in many installations over the years and has resulted in the issue of "decimal dust". Fractions of batches left behind as a result of conversions.
There is no real solution for this other than to revaluate your UOM's and conversion factors. Can you make the Base UOM M2 and make the SHT as an alternative UOM? You can still order in SHT but your QM will be done in M2 and should be closer to being correct.
This is not an easy thing to resolve for certain materials. Good Luck.
Craig