I haven't made this shawl but I took a look at the pattern. Did you count to see if you had the correct number of stitches at the end of section 1? If not, check the following: in Section 1, the shawl increases by 2 stitches every row except in rows 13 and 24 where you do a double yarnover (YO2) and those rows increase by 4 stitches each. You can check if you did this - the double YOs will be larger than single YOs. You could also could have missed YOs at the beginning and end of some rows. The edges should have a line of YOs running evenly along it 2 stitches in. If you frog back, you may want to count your stitches at the end of every row to make sure if you have the right number before starting the next row. Good luck.

Forgot to mention that you can frog/tink back one row at a time and check your stitch count against the counts given at the ends of each row in the pattern in section 1, if you don't want to frog the whole thing. It's more tedious than starting from scratch but this way you might be able to spot where you went wrong and avoid the same problem.