Try Best Press on your fabric and iron before cutting.
Make sure your ruler doesn't move: sandpaper dots or invisigrip or whatever.
Make sure you are holding your rotary cutter correctly.
Check your machine for the 1/4 inch or scant 1/4 inch, and the pattern for what it calls for as seam allowance.
Use the same ruler throughout the project. Also, use the same machine for the project. Changing either can result in uneven work. Guess how I learned this?
ali