You aren't a failure! And it doesn't matter really how much you're practising, i think it matters more at this stage that you're practising correctly! 10 second cross and 30 second f2l probably means either:
- you're spending too long finding the pieces. this will probably get better with more solves, as you just need to get used to isolating the F2L corners and edges, and knowing where all your cross pieces are.
- you're using way too many moves. This requires more thinking - like GuRoux said, do plenty of untimed cross solves, and work on things like solving multiple cross pieces at the same time/setting up the next cross piece. Then do plenty of untimed f2l solves - look at things like f2l 'alg' lists and reconstructions of solves in order to see how you can increase the efficiency of your f2l.
- you're turning very slowly - it might just be that you're not confident with what you've learnt, in which case doing solves will probably help. otherwise, just generally work on your fingertricks and stuff
Keep at it!