A good instructor will keep moving you onto different exercises before you really feel you've got the hang of the last thing. I remember when I learnt to fly that I never really felt I had practised each new thing sufficiently. Now I look back I realise that my instructor was doing the right thing.
By moving onto the next thing you start to learn a new skill but are of course still practising the ones you learnt before. If you did each one until you were perfect at it then you'd probably take 100 hours rather than 50. So rather than just bash on flying around your instructor has started pattern work.
Just think back how far you've come, I assume you can take off and fly around OK. I bet that seemed strange when you first started.
Its also quite normal to get stuck with something. My problem was steep turns. We just moved on to other things and then came back to them and they clicked into place.
Rely on your instructor, if he/she says you're a natural then they are either correct or flattering you (or both). They have seen lots of students and can set the pace as required. Its fairly normal to feel that things aren't going well but if you ask your instructor then they'll probably let you know how you are doing.
One thing that many schools do is to let you fly a lesson with another instructor who can then give you an independent assessment of progress. You could try this.
Don't forget to enjoy it though!!!