need help making a marble cake

[alarosalpn]

I am making my neices bday cake and she wants marble... I found cake mix at PriceRite for $0.89 each.. I have 3 chocolate and 3 vanilla. I'm using a 12x18x2 wilton pan. I know it holds 3 boxes...
What I don't know is how to swirl them together... I'm very nervous about messing up on this...
I plan on making all 3 boxes of each flavor so I can use equal amounts of each in the 2 layers...
Can anyone explain to me how to swirl them to make it a marble cake?
Thanks!
Amy

[nuisance26]

~This is how I do it:
Put one flavor/color batter in your prepared cake pan. Then add dollops of the other flavor/color. It should look like a domino piece. Then use a butter knife to make a soft zig-zag pattern through the batters from top to bottom and then from left to right. Be gentle and don't scrape the knife along the bottom of the pan. Just swirl twice! Any more will make the cake look muddy not marbled.~

[alarosalpn]

Thank you!
how much of the "domino look" flavor do I use? Would it be 1/2?
(ex: pour 1.5 prepared boxes of vanilla in, then dot with 1/2 box of chocolate? or would I use the whole box?)
How much space should I leave between the dots? Would I do it with like a 1/4 cup?
Ugh, I think I'm worrying about this too much. lol
Thanks so much for your help

[nuisance26]

~Good guess! It's generally about 3 parts of the main color to one part other color.~

[alarosalpn]

Thankyou! I guess on layer is going to have more vanilla than chocolate and the other more chocolate than vanilla cause I bought 3 of each! lol oh well, it will all balance once it's put together and decorated.
Thanks again! You saved me today!