Seems you are asking if your clan affiliation traces back partilinially(sp?), or martilinially(sp?). Well, to be honest it goes back in both directions. You can't change who you are, or where you came from. Does your fathers family have a tartan, or are they affiliated with a clan? I've got a friend of English descent, yet his family history has ties to clan MacKinnon. If there is a connection on your fathers side you could join the clan assoc. of that clan.
As your mothers side has a MacDonald connection, you could most certainly join their clan assoc. too. You could join both clan assoc's if you wanted to.

As for wearing this tartan, or that tartan, don't worry too much. The main thing is to know about the tartan you've chosen, and wear it respectfully. The tartan police don't exist. You won't be locked away if you wear a tartan that doesn't have a connection to you. Lots of people want their tartan to have some significance, and I understand that, as I too feel that way, but it's not a rule. Knowing your lineage as you do you won't have any trouble wearing MacDonald, or what ever clan tartan your fathers side might be associated with. People will ask the significance of your tartan, and just as you've explained here you will explain again.

Welcome to the addiction.