You don't want to stretch anything if you can help it—it seldom looks good, but if you do want to resize a layer, select it, then go to Edit > Free Transform (Ctrl+T). When you mouse over the little box at one of the corners of the layer, you'll get a diagonal double arrow icon; that indicates that you can resize in both dimensions. Hold down shift to restrain the shape so it doesn't distort. Alternately, you can enter exact values in the tool settings bar.
Once you've got your lines over the paper, play with the blend modes a bit. If you've got black or dark grey lines, I recommend using the multiply blend mode; it usually does a great job of making the lines look like they're drawn on the paper instead of having been placed above it.
If you decide you need a larger paper texture, do a search in the tutorials forum—I seem to recall that there are a number of good tutorials on creating distressed paper and parchment.