K, the advice so far is ~ what I'd have said (I thought the wallpaper roller was my idea -apparently I'm not the only one to have both wallpapered and applied liner patches ) Be sure to 'round' the edges - as per Carl's sug. Cut the new patch ~ 1" bigger than the previous one, all around, use the roller to seal the 2nd patch from the inside part out to the edges, you want to see the glue 'sqeegeeing' out from the outside edge.
Is there any chance that this 'rip' is at a seam? If so, you may have seam seperation and the manufacturer should replace it at ~no cost to you (the warantee is 'pro-rated' so you may have to pay 5 - 10 % of the cost). Using SCUBA gear and applying the patch 'continuiously' will net you better results. I've seen pools that I've patched still holding just fine after 5 years - so, if done properly, you don't need a new liner
Hopefully, this is of some help/ reassurance to you - Waste