There is no gramatical difference. Gern or gerne... Both of them are same. That's why dictionaries show them as 'gern(e)' instead of seperating them. But people prefer gerne if they want to stress on the verb, but it's not gramatical. Btw., do not forget the last e in a german word has low stress, like half pronouncation, so they sometimes remove it. As a result, it's just your choice to use gern or gerne

According to my German teacher they're the same and it's just a matter of preference.