next time.. let the cotyledons form before u start prying seed open, see that they are developed, first.. they'll push teh shell open further and make it easier too... if taken off before cotyledons develop it's not a good thing. the less we do the better... often fiddling makes things worse. wait for the shell to be easily removed with a couple small tweezers or soemthing. hold one side ensure it is only the shell you are secuing and pull on other half very gently at widest opening. if difficult wait longer.
was this papertowel method? that can lead to seed sheels not popping off as easily... or if sown in very loose substrate or too shallow the shell is more likely to stay on. don't ove do that last part though if adjusting... better it has an easier path than a extremely tortorous one to break ground. but, the substrate will catch it and tug it off better in some cases without causing any added time to sprout.
anyway, you can do things that will reduce the likelyhood of this occurring.. just becareful not to go too far.. pulling of a shell shouldn't be a problem in most cases.