It was a SIN!!!!
And those nuns struck the fear of God into you about it. They had you thinking that God would strike you dead for doing something like that to Christ's body.
Isn't that really peculiar since we have a Catholic priest here telling us that the word used in the scriptures to command us to eat the flesh of Jesus actually means to gnaw, rip, tear, chew and grind the flesh of Jesus before we swallow and that proves the verse is to be taken literaly...
The nuns were WRONG.
If a person allows the Host to dissolve completely in the mouth, and never actually swallows any part of the host, he does not receive the sacrament.
This happens much more rarely nowadays, for three reasons:
1) the hosts themselves are more substantial, and do not dissolve so quickly without chewing and swallowing;
2) People are no longer mistakenly instructed not to chew the host;
3) Many people receive under both species.