Easter Day debacle

Hey I'm fairly new to brewing but I have a couple of questions regarding my last batch. I planned on brewing a black ipa yesterday night and was all ready in the morning because I knew I had plenty of running around to do during the day. This was my first time using liquid yeast (wyeast 1272 american ale yeast II). I got home and started brewing and then realized I had pulled out the wrong yeast pack. I figured no big deal and pulled the right yeast pack out and figured I would wait until it was ready. I finished brewing and cooled the wort and transfered over to the primary and covered it with aluminum foil until the other yeast was ready. I checked my OG and I was dead on at 1.072. After reading the back of the wyeast pack I noticed that it is only recommended up to 1.060 so I would result in under pitching. I should have either pitched 2 packs or done a starter but I didnt do either of these, is it ok for me to pitch another wyeast pack now? Also it has only been 18 hours and I havent seen any signs of fermentation, should I be concerned ?

It won't hurt to pitch another pack of yeast. The earlier you do it the more effect it will have. You did underpitch, and that is why you don't see any activity. You may get some minor off flavors from underpitching, but in all likelyhood the beer will turn out just fine in the end.