It's also possible that the pattern
contains an error. I, too, added up the stitches in your original post and reached 29. A cast-on of 30 stitches, in that case, would be an error.
Does the pattern provide a chart, or are all the instructions written out in words?
If there's a chart, count the boxes in a couple of rows to see whether there are 29 or 30 of them.
Also: there are many
patterns on the Net that haven't been tech-edited, or sometimes even test-knitted and/or proof-read.
Did you check other patterns by this designer to see whether there was feedback on them? Ravelry is a good source of info on designers and their patterns: are the designs good? are the instructions accurate
? and so on.
Hope it works out soon.