I wouldn't be too worried unless this continues to happen after a few rides. I just put a new clutch in my 125 last weekend, and it would also roll forward a little bit when I put the bike in gear with the clutch pulled in at first. This is because the new plates are sticking together some. I am guessing you didn't soak them in oil for a few hours before installation? Regardless, after the plates get a little use, I would expect the problem to go away and the clutch to act normal.