Traditional-to-Micro-SIM Cutting Conversion Failure?

I have gotten my grandma's old iPhone 4 and I my previous phone was a iPhone 3GS. I'm unable to switch the SIM cards for the iPhone 3GS uses a normal SIM, whereas the 4 uses a Micro-SIM.
My mum and I have tried cutting it (we saw in a YouTube video that you could just do that and it actually worked for the person in the video) but we have actually cut it a bit too small so now it has space to move around which is bad.
An idea we have is to tape it in place with sticky tape (not on the metal part) so it can't move. Will this work or ruin the SIM card, iPhone or even both?
Kind regards.

- L

Added (1). I mean to ask: will it or will it not work?
Ignore the "or ruin the SIM card, iPhone or even both?" part.

Micro