Goodluck! I found with the dip tests, they're super super faint and don't progress incredibly fast. BUT, when I thought I had a very OBVIOUS negative, I for some reason, looked at it the next day once completely dry and something was there!!
So I took another and this time something quite faint but with the tiniest colour showed up!
Check yesterdays test now, is it any darker than when you took the photo within the time limit?? The dip tests usually take 5 whole minutes rather than 3 to develop too!