it prbly has 100mg or 90mg of dxm based on the information you gave. you could consume the entire amount.
the thing with disassociatives is that it kind of gives u a different way of perceiving body, things seem novel and different, you can drift into interesting way of thinking, time may slow down, vision may be slightly altered in some way, motor coordination is affected at higher doses (200mg+)
if you have social anxiety it isn't going to make you feel like a social butterfly and the experience may either be better or worse than you expected.
but if you are desperate to have some kind of altered state of consciousness or simply to try and get out of your head in some way, it can't hurt.
i used to dose 150mg before going to school, even before an english exam. nobody seemed to catch onto it.
it is worth having a small amount of ginger before you ingest the syrup just to ease the stomach discomfort or nausea which may come.