Which is the pattern? Top, or bottom, piece? I have routed pieces about that size before, always with my master (what others call patterns or templates) on top. My masters are two 1/2" plywood pieces glued together. I see you are using nails. I use nails also, but my master nail pilot holes are usually about 1/2" apart, and I would use at least 4 nails in a piece that size, and add more nails if it seemed to be shifting. The 1" master give me a solid grip, and I use both hands - being very careful about keeping my fingers away from that whirly part, shifting my hands very frequently, and taking very shallow, and short, cuts. I'm not had any issues with my method. However, what you picture is about as small as I will willingly go without some how clamping the piece.
Disclaimer: Just because I do it this way, does not mean I recommend you do it the same way. Different background, different experience, and all that.
"It ain't what you're told, it's what you know." - Granny Weatherwax
Some days, the supply of available curse words is insufficient to meet my demands.
Call me a craftsman, artisan, or artistic, and I will accept that. Call me an artist and you will likely get a quite rude comment in return. I am not a @#$%ing artist.