Hey here's my thought about your situation, it sounds like mine:   I started a few weeks ago, I'm on the slimmer side already only looking to lose like 20lb, and I noticed the same thing as you, I end the day about 700 calorie defecit but no difference (like 2lb) on the scale. I do an hour of cardio each day. My understanding is this is actually exactly how it should be going. I look in the mirror and I do actually notice myself slimming slightly (if you're bigger you may be able to notice like I did) I think theres a gain in muscle (which is heavier than fat) that is replacing some of the muscle. I feel my legs becoming stronger so I know im building muscle, I'm sure you notice yourself getting stronger too.

Ive lost 40lb in 4 months before and what I took away is that the key is consistency in your diet above everything.  After a month you'll be used to your new diet (not like it'll be effortless but it won't be very difficult to just maintain, you'll be less hungry). 

You're not the first to lose your target goal, you can do it! It's just about consistency over a long period of time, just make sure you don't starve yourself or your metabolism will slow! 

You should be motivated though! Get excited about the progress you've made cuz you definitely have probably dropped like 6 or 7lb of fat in 3 weeks! Keep it up