I wouldn't use freezer paper to make bias stems. Here's my method, which requires using a Clover bias tape maker in the size you want. I've tried other brands, but Clover brand with its color-coded sizes works best for me.
1. Heavily starch the fabric before cutting into bias strips. I "paint" a 1:1 solution of Sta-Flo liquid laundry starch and water onto the fabric with a large wall-painting brush, toss the saturated fabric in the dryer, and iron with steam.
2. Cut fabric into bias strips of the correct width and piece these strips together on the bias to make one long strip.
3. Place a large, long pin in the ironing board cover creating a space for the finished bias tape to run under.
4. Thread the bias through the Clover tape maker, iron it as it comes out, and thread it through the pin in the ironing board.
5. Basically I place the iron on top of the bias tape before it goes through the pin. The Clover tape maker is to the left of the iro,n and the pin is to the right of the iron. I pull the tape through the pin with my right hand and hold the Clover tape maker with my left hand. The first few inches of the tape is always a little sloppy, but all the rest of the tape is perfect. You can make yards of bias stems this way in just a few minutes if you have done all the prep.
The advantage of bias stems made this way is that they are fairly stable but still fully flexible for shaping around curves. When I have a choice, I sew around the outside curves first where the bias stem needs to be stretched.
This method gives me the most accurate finished bias stems with the least amount of work. I tried bias bars in the past and burned my fingers on the metal ones; plastic was better. Also tried doubling the fabric, sewing to the background, and trimming before folding over to sew down. With both methods, I didn't like the extra bulk inside the stems. I also didn't think they were faster or less work than the method above. HTH!