Today I made my first 14" square cake. I don't have a core heater, so I tried the flower nail trick. The cake rose so much, that the nails disappeared! 

It's a good thing I read the instructions that came with the cake pan, that said use 16 c of batter instead of the chart I found somewhere on here that said 19 c!

Anyway, how am I going to get the nails out? And how can I level a cake that large?

When you flip the cake out of the pan, the flat part of the flower nail should be on the bottom, so just pull it out. 

To level the cake, take a length of string or dental floss and hold taut and run along the edges of the pan. Cuts through without a problem.

Yes on both comments. Dental floss trick works well. As doz posted Keep floss tight and taunt. 

Thanks so much. I was totally needlessly freaking out about my disappeared flower nails. Of course they were on the bottom. *facepalm. 

Thanks for the dental floss trick. I will give it a try.