It took me a while to get the strips to sew staight. I finally took a post it note pad and measured on my machine where 1/4inch was. I secured the pads so that my fabric butted up to the post it notes. This helped keeping the fabric straight I still use them today but I purchased some purple plastic strips there are not as good as the post it notes. Give it a try it might make a difference! Welcome from Sammamish, WA!! I will take a pic so you can see what it looks like!
It may make the blocks / pattern bigger than expected if you use the 2 1/2 strips