You did an excellent job matching the stripes on those squares! I can't even match stripes on straight grain of fabric, say nothing about bias!
If you spent $30 on shirts, you may want to seek another thrift store -- that seems like a lot to me. I'm lucky enough to have found a thrift shop near my mother's (I visit her two or three times a year) where I can sometimes fill a paper grocery bag for $3 or $4. If they have lots of 100% cotton shirts, I stock up.