New Aurora strings that don't fit on my Soprano, help

Hey all, so I just got some new Aurora ukulele strings. I was so excited to slap these babies on when they arrived in the mail. Now to my disappointment, the 3rd C string doesn't fit in the slot on my Kala Soprano uke. Uke republic sent me a set of concert strings and they had a sticky note on them saying that I could put these on a soprano. So what do I do from here? How would I go about filing down the slots on the nut? What effects could that have on future string changes? The first G string fits decently with just a bit of newly developed buzzing on the first couple of frets. Could that be caused by the concert sized strings? I'm leaving the first 2 strings from my old set on until I figure out what to do.
Thanks in advance

Take care.

Are you sure you don't have the G and C string reversed?

I'm sure I haven't reversed the strings, the G string is the orange one and the C string is the purple one which I can't fit in the 3rd string slot. I don't think Aurora would reverse the universal string numbering either so I'm really quite confused.

How important are these new strings to you? What other strings have you tried on the uke? You could widen the slot in the nut for the C string at the slight risk of buggering it up. You could use a welding torch tip cleaning kit to do that.
http://www.homedepot.com/p/Lincoln-Electric-Oxygen-Acetylene-Torch-Tip-Cleaner-Kit-KH575/100341101 They're like tiny round files.

Matt Clara said:

How important are these new strings to you? What other strings have you tried on the uke? You could widen the slot in the nut for the C string at the slight risk of buggering it up. You could use a welding torch tip cleaning kit to do that.
http://www.homedepot.com/p/Lincoln-Electric-Oxygen-Acetylene-Torch-Tip-Cleaner-Kit-KH575/100341101 They're like tiny round files.

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I have always just used the normal soprano Acquilas. I decided to tighten the C string up to see what would happen, it still makes a noise and I can get the open string to pitch. But it does make quite a bit of buzzing now.

The open strings are even buzzing now. And I can't get my first string up to the right pitch, it just keeps dropping back down no matter how much I turn the tuning peg.

If the the strings are buzzing, you probably have to raise the action at the nut. Any competent professional guitar tech can do this for you at a reasonable cost.