You can get 6 good size scrubs wash bags from a single flat sheet. You are aiming at something around pillowcase size but Im making them a bit bigger if I can. They do all vary in size.
Start by folding your sheet in half length wise, then in half length wise again. Get the edges as close to even as you can and smooth out all the wrinkles.
I mark off the length of the template from the top and then fold down the top. Align the edges to give a right-angle and cut across all layers level with the folded over top.
Next, the strips you have need to be cut in half the easiest way I have fond of doing this is to just cut down the fold that's the same side as the edges of the sheet.
Next, for the 4 end pieces you can just fold right sides together with the original hem as the top of the bag and hem and zigzag or overlock down the side and across the bottom.
For the centre 2 pieces fold over the top about 2 in or 5 cm on the inside and press.
Then fold right side together, so the fold is on the outside.
Next you need to make 2 button holes for the drawstrings. These need to be positioned so you can turn a wide hem down over them to make the bit for the drawstring and they are on the outside of the bag. I have done them different ways but think the best way is horizontally about 1.5in or 4cm from the top edge, you may have to alter this depending on your sheet hem width. It is easier to sew a button hole on a double thickness but it does work on single.
You need to put one close to your side seem
Then mark the centre and do the second on the opposite side.
You need to carefully cut up the centre of your button hole with sharp scissors or a stitch ripper (I use a scalpel but it's a bit dangerous)
When both are done turn the top over to the wrong side (outside at the moment) and press.
Next hem round the bottom of this turning.
Now you just need to thread in the drawstring. You can use bought tape, or home made tape or cord, but it should be able to stand lots of hot washes so cotton is best.
I use an adapted large cable tie as a threading needle but a nappy pin will work or a long stitch holder for knitting.
Do the same again through the other button hole.
(they are bigger than it looks in the photo below, its hanging off the ironing board)