Well thats gotta be nerve wrecking, but i went through the same thing as well. My suggestion is to wait a couple days and try it again... and when you take the test try to be sure your urine is a dark yellow... so make sure not to drink a whole lot the day you decide to take the test. I know they suggest taking the test in the morning as for your HCG level is suppose to be "higher" but that isnt always true for all women, everyone is different, it may work better if you do it at night...or just try opposite of whatever time you have taken it. If you still dont get your period in the next couple days and that test still doesnt become positive.. he best way is to make that appointment!
I wish you the best of luck with everything!!