Strings don't fit at the nut.

[cyprus]

So I just bought a set of Roto flats, the Steve Harris ones, and these things are huge. I new when I bought them that they were gonna be a heavier gauge, but geeze... I got the G string in, but the D barely fits in and is pretty much resting on the nut. I'm fairly certain the A and E will do the same.
So what should i do?
Obviously, I have to make the slots a little bigger, but I don't have the money to buy files.
Any suggestions?

[Slowgypsy]

Some suggestions...

Just buy one file, for the smallest slot. You can carefully use that file to enlarge the other larger slots. It's not the "Stew Mac" way, but if you go slow and careful it will work just fine.

Another suggestion I've heard about but never tried myself is to get the correct sized drill bit (way cheaper than the correct sized file) and sort of use that drill bit as the file. Running it back and forth, manually. Again, I never tried this method myself but it seems sound.