Are you drawing diagonal lines on your 2½-inch squares? I found that I needed to stitch just the side of the line that will have the fabric cut off. This allows just a smidge extra of fabric to allow for the fold over. That way your folded over square edges should meet with the corners of the rectangle. Oh, and make sure the diagonal stitching line is straight. Sewing more slowly may help.
SandyQuilter

Mine got a little better as I took more care when pressing and didn't stretch the gooses leg!

The easiest way to make any size flying geese can be found at www.patchpieces.com This website has a No Waste Flying Geese method that is wonderful. You can use it for any size flying geese just plug in your finished size measurement and then cut your squares. You will make 4 at once and all the same without cutting off any waste.
Enjoy!

I bought the Eleanor Burns template on Flying Geese and I'll be darned but they worked great. I used to be really awful, cutting off the points, wonky blocks, you name it. But not anymore. I can actually make one and have it turn out OK. I think Fons and Porter make the same kind of thing too, you can buy them at Joann's.

fore you sew the sq. onto your rectangle...make a mental note which part of the square you
will be keeping and which you will cut off. Sew just a scant more into the cut=off side as on'
the side you will be keeping. Then proceed as usual in trimming off the unused portion. For me
just that 1/32 nd of an inch (just a hairline) extra on your saved triangle will allow for the little
bit you usually are short. I hope what I'm saying is clear. It makes a world of difference for
me.

E Burns has the best method and not hard at all just need there ruler

it works great and love eleanor burns method and really it is great. rulers are in joanns and I got mine with 50% and that is when I tried her method. love doing her way..works for me

I always paper piece my flying geese and they are perfect everytime. I have a PP pattern and I enlarge/reduce it as needed.

I paper pieced my flying geese and they came out perfect.

Ricky Tims has a one seam flying geese that works wonderful. google for the tut.