Things I do to help prevent this.

Cut borders on the straight of grain. (I understand this is the back of the quilt, so this probably doesn't help this.

Pin-baste like CRAZY! When you think you have enough - add more. Every 3-4 iches.

Use a walking foot. BIG help!

Most importantly, let the machine do a lot of the work (this is where the walking foot helps). No pushing. No pulling. Just assisting to make sure the bulk makes it to where it needs to go. I find when I'm in a hurry (at the borders and the quilt's almost done - nothing like seeing the light at the end of the tunnel and you want to run to it instead of walk...) I start pushing it through and I end up with wrinkles.

I'm constantly reminding myself to relax during this stage. I get soooo excited that my vision is almost complete....

Wow, for me being a new quilter for the past 8 months, you call that a wrinkle? You should see some of my really early wrinkles, and not just on the quilts either...

when you add sashing to a quilt you need to measure each side and average the measurement then make it fit don't just sew the border on cause you can stretch it and one side could be longer than the other. I learned that one the hard way. I'm not sure if that is your problem but I know each side's length can very and they need to be the same. Measure the edge while it is laying flat and don't stretch it.

I also divided my border in half and marked that point - If I was using 12 inch blocks, I also marked my border in 12 inch increments.

This improved the odds a little bit.

I agree on the measuring to make sure you are not making the borders too big. But sometimes you don't have your fabric layers stretched and as you pin you are creating tugs. So after you pin, pin, and pin baste. ( Pinning very close is very important)!!!! Turn your quilt over, it still should be fairly flat even with pins and you will see if you have a lot of tucks. if so turn over and fix those tucks now before you quilt. Also I hardly ever use a even feed foot but some people need it. Don't pull or push the fabric let the machine do it for you. I do hold my hands right before and after the fabric at the needle area, just to keep everything flat and spread out. Some machines may need the presser foot pressure to be loosened, especially for a newer quilter. If normally it is on 4 try 3 or 2 1/2. Practice makes better. The more you quilt the better you will get:-) Bernadette

wait...I am confused...one post said sew two lines in Different directions and the other said I have learned sew in same direction...which is it? not sure I understand. Margie