It should be OK. Either you can print a template from a website, or you can buy a cutter very inexpensively on eBay. I've heard that some of the phone stores will cut it for you, or if you are a customer will give you a microsim free.
Why not just get a micro Sim from your carrier? Most will perform the exchange for free.
If that isn't possible you can cut a mini Sim down to size, assuming the Sim is new enough. I've found the the chip on some older sim cards is larger, making it more difficult to cut down.
I've seen stencil kits you can download and print out. The preferred method would be to buy a sim cutting tool. Amazon sells them for under $5.
I borrowed a cutter.
It cuts cleanly enough that you use the leftover as an adapter to go back up in size.
Less than $10 on Amazon, and usually comes with adapters.
Waiting for a Nano cutter now, gonna try the same thing.
FWIW, it seems that most (many?) cell phone stores keep a SIM cutter behind the counter and will use it upon request. Just walk into a store and ask, "Could you please cut this SIM for me?"