Couple possibilities of what causes such surprises - not a fix, just ideas.
- Adding data that doesn't fit, though you say you didn't. Typed spaces, instead of deleting cell contents, are data, don't forget.
- Adding borders or colors all across the board instead of a small range - people do that often, color pink entire row or column and add borders all across the board
- Change of printer or font - some fonts look ok in print preview and don't fit on a printer page
- Data that you think is not there may well be in the lower right corner far away from what you think is there - try View > page or something similar so Excel can show you where it'll page.
- Changed page setup reduction from some number less than 100% up
If you can't fix it, copy contents to another sheet and reformat. It often reduces the size of file and is a tipoff that a huge range exists where it shouldn't.
I don't follow "the rest of the cells are grey", nor the "blue border".