As the others have said - if all your blocks are the same size and fitting together okay - not to worry

As Skeat says - Some patterns have errors in them - I also learned that the hard way - now I have more confidence in myself and know that the patterns and/or instructions are not always 100% accurate.

Susiequilter is right, if you're making half square triangles. To make a HST, you have to start with squares that are 7/8 of an inch larger than the sides of the triangle that you want. So, if you want to get a 2.5 inch block from two HST's, you will need to start with 3.375 inch squares rather than 3-inch squares.

However, if you were so lucky as to have all the other parts of the block come together evenly after the mishap with the HST's, then I agree with everyone else in that a couple of inches in length and/or width won't matter in the long run.

When I make half square triangle blocks I sew two strips or two swatches together then lay the template on the seam and cut out your half square triangle block. You will get an accurate block if you cut accurately.

If you are making a lot of them of the same colors just cut out two strips and sew them then cut out all the squares you can then pull apart the strips and sew the other sides together and continue to cut out half square triangle blocks. You won't have to cut out any triangles as they will show up when you cut the square out.

The waste is minimal if you snug up the template to the last one cut out.
Any waste is well worth the effort for the accuracy you get.