Hate hearing this happening to a beginner cause it's so discouraging. sounds like you will either have to cut down the strips and make smaller blocks (say from 12" to 9, etc) OR change the pattern to use these in smaller cuts--either way you end up needing more fabric
Many of us rarely use precuts, instead opting for yardage which we cut to size, as you avoid this problem plus your fabric can be more versatile.
Citrus suggested a string quilt--you can use various wides of strips for these, google them and see what you think. Also google "Easy Peasy" quilt--it's a type of string quilt that uses strips in larger blocks that you then cut diagonally (use spray starch to avoid stretching them) and realign to get a neat block--my avatar is one that I made as my 2nd quilt.