You are wrong. Gum is noncountable in English. We do not say "a gum". You can make it countable by saying "a piece of gum", "two pieces of gum"....
Correct: Would you like to have a piece of gum? Correct: Would you like some gum? Correct: Would you like any gum? Incorrect: Would you like to have a gum? Incorrect: Would you like a gum?
It "might" mean both, but essentially because of the preposition في (in), the natural way to think of it is that the chewing gum is just (in) the bag - not smeared or anything. Typically expressing the thought of a chewing gum being smeared would require another wording and formulation, .e.g. stuck ملتصقة or anything like that to convey the idea of being smeared (this is beside using the proper position, whether it was smeared inside, outside etc).