A japanese friend wrote that to me and Im not sure what 'watasi ha' is. Is this another form of 'watashi wa'? Im just a struggling beginner trying to get a jumpstart before hopefully taking my first class next semester.
You're right, the thing is that they don't strictly distinguish "shi" and "si" in Japanese language. So you can write "し (shi/si)" in either way, although "shi" is the correct one according to "Hepburn system", which is the standard romanization system of the language.
I don't know how they teach Japanese in the US, but probably you will learn the AIUEO table and you'll see that there're about 10 basic consonants, one of them being さ行 (column S). In the column S they have 5 characters: さ SA し SHI す SU せ SE そ SO. And as you see, somehow they are putting "sh" consonant and "s" consonant altogether in the same column. So it's no wonder they mix up watashi and watasi. I'm not sure if this explanation would work, but anyway, good luck on your class!