Your best bet in a harm reduction sense would be to snort appropriate amounts with your remaining dope, and cast IV aside. Though if you really want to, if the timing is right, I would save IV for when you wake up in the morning. In my experience that is the best rush, get the most out of it, etc. Or, if not in the morning, IV only when you are not already high to get the best rush / feel.
And as always, the longer you can wait between doses the better. This is good for tolerance as well as making your dope last longer! (Who doesn't love that?) Everybody and their mother who starts dope says they don't want to / won't become a junkie, though inevitably MOST do.
Back to IV'ing, in the sense of safety stick to what gets you high.. don't try to push it too much looking for that extra OOMPH.. known too many who thought just a little more wouldn't kill em, but it did or almost did. Just my input and words of wisdom

Above all.. enjoy while you can!
Last but not least - when you finish that little amount and tell yourself you won't get more, more than likely you will think maybe just once more.. when that happens, tell yourself NO!