If a set of Marketo Demographic and Behavior scoring fields exist and you then go and create SFDC Demographic and Behavior scoring fields, they will not automatically link together.
The real question here now is, how many Demographic and Behavior scoring fields do you have in Marketo due to the creation of these fields in SFDC? If you only have 1 set, this means that the fields you created in SFDC are not synced to Marketo because they are not visible to the Marketo Sync user. If you have 2 sets (or duplicates) this means that the fields you created in SFDC did indeed sync over. 1 set should be synced and mapped and the other should be Marketo only fields.
If you have 2 sets, you're going to want to ask yourself which set you are going to be using. If the original unmapped ones are what you choose, you need to contact Marketo support to have them mapped.
If you only have 1 set, you won't even able to map them anyways because the fields you created in SFDC are not visible to the Marketo Sync user. Therefore, you need to make them visible first so that they come over to Marketo as the 2nd set.