I don't believe they'll give you two at the start. I think the size of the sheet was a little bigger than normal, but not quite legal sized, so that'll give you a little extra space. One thing to keep in mind is that the proctor won't always really be paying attention, so there is the possibility that you'll have to wait to get a replacement sheet. Maybe try to strategically time the replacement, like raising your hand while working a problem that doesn't require written notes.