Salam alaikum dear sister,
Well, to begin with I'm not a scholar, but there's this hadith which says,
There is no marriage contract except with a walee and two witnesses.” (Reported by al-Tabaraani; see also Saheeh al-Jaami’, 7558) If u are a convert and have no walee , then a sheikh or a judge should be a substitute. The fatwa that
sis Shyhijabi has posted states that the waliy should be there to accept the proposal in the first place, but if ur father or uncle or whoever can be a wali is not a muslim, then u will need a sheikh instead. In all cases, do not rush this marriage unless u make sure that it's 100% halal. You can have a look at this fatwa as well
http://www.islamqa.com/en/ref/2127/شروط صحة النكاح
One more point to raise, did u ask the groom why he insists on having just two witnesses? From what I have come across in life, such guys are mostly after having a nice time with the girl on the grounds that this is a " halal " marriage. THey are mostly unwilling to bear the responsibilities of a documented marriage and according to
some scholars , such a marriage is equivalent to zina. I just want u to make sure of his intentions before u go on with this marriage. I'd rather u ask the sheikh of ur local mosque, he will probably give u the right answer to ur question. May Allah make things easy for you and guide you to what pleases Him in this life and the hereafter. :tti_sister: Ameen.