Straight pins? Yikes!!!
If you have some extra batting and backing and fabric, I would make up a test sandwich to practice on. Assuming you are using a walking foot, my bet is that the weight of the quilt is creating drag and that is why you are getting those tiny stitches. However, it could also be the sandwich itself, which is why I recommend creating a test sandwich. Did you lengthen the stitch?
If the problem is drag, then you need to rig up something to hold the weight of the quilt. One common practice is to place an ironing board to the left of your machine, at the same level as your machine. Is your machine sitting flush in a cabinet so you have a large flat surface to work on? If it is sitting on a table with just a small surround, you are going to have problems feeding the quilt evenly without drag (it invariably catches on some corner of the little table; do not ask me how I know this). In that case you may want to create a styrofoam surround for your machine. I used the Youtube videos on how to make an inexpensive sewing/quilting table to do this.
To be honest, I would never attempt to quilt something this size that has been basted with straight pins. It would be worth the time to replace each straight pin, one by one, with a safety pin. (When quilting on my domestic machine, I have always spray basted but I'm not sure how well that works with a minky backing.)