No. They may take one of them, but if they do that they will continue to stamp the remaining one you have. However, it is advisable to travel with a copy of it in addition to the two originals they give you. That way, if the airline or the port of entry asks to keep one of them after looking at it, you can ask if you can give them a copy and keep the original yourself for next time, and for their records they will usually accept the copy (but you still have to show the originals, of course). Normally you have to present both sheets (or all 3, if you were issued 3, as I was), so if you can avoid giving away one original that is better.
Be aware that when you arrive in the US with Advance Parole, you will be sent to the secondary inspection room (unless you go through US immigration before boarding the flight, like what happens in Toronto). Your own questioning should take less than 5 minutes when you reach the front of the line in there, but sometimes that room is busy with people with questionable immigration status, you could end up waiting more than an hour there. So if you have to go through immigration after initial arrival in the US but before going to your connecting flight, make sure you have at least 2 hours between flights so you don't miss the flight as a result of going to secondary inspection.
Yes you can go back now. But with your interview being this month, you might get the card or at least an I-551 stamp in your passport before you leave, so you wouldn't need to use Advance Parole.