When you add the side triangles, if you don't get them lined up just right you can lose some of the length of the block :wink:

Working on the bias it can stretch. Also, if your original cuts and stitching aren't exact it can affect your outcome.

When cutting the corners for something like this, I often cut the trangles larger on purpose. Then I can square them up and the block will be perfect.

Is this the block from the tutorial PatriceJ did?

She said it tended to get "wonky"

Good idea ,

http://www.shirleyannesheart.com/200...neapple-block/
I think my problem is using shirts and clothes so selvages not clear

Sawsan when you cut out each square block each time make sure it is the same size as the one you just done and make sure you always use a 1/4 " seam, then also iron each square flat
after each new square is added on.
On the one your have done above I would take your ruler and
square up the top to match the bottom and cut your ears off that is sticking out on your square you have shown. :D

looks like needs more accuracy in piecing.

First, starch the fabric before handling it.
Second, cut carefully and precisely, so that the next square is exactly the size of the one you just finished.
Third, sew exact 1/4" seams to prevent losing points and to prevent uneven/wonky seams.
.

A couple of tips to avoid this in the future, Cut your triangles a little larger than what the pattern calls for. Then trim to size with a square-up ruler after adding them.. Do not stretch to fit, that bais will give you fits. And do not iron. press. Ironing you move the iron back and forth across the fabric. Pressing you just set the iron straight down, and then lift and press again in another spot. ironing distorts the fabric

This is one of the best tutorials I've seen on starching fabrics. I have used this technique many times and find it really helps in preventing stretching. You do not need to wait for it to dry but running your hands over the fabric after you spray seems to really help keep the flaking down. Give it a try and see if it helps you. I find it very easy and effective. Makes my fabrics look great. http://www.daystyledesigns.com/starchfabric.htm