Mistakes happen. Fixing mistakes is probably one of the hardest things to learn. You've only been knitting for 6 months, it takes time to learn and develop skills. Relax and give yourself time. The more you enjoy it the better you learn.
I've only been knitting for a little under a year and a half and am far from being expert at knitting. I learn a little bit more every project. Some mistakes I can fix, some I can't. I just accept that and do the best I can. Heck, some mistakes I just let go and move on because odds are high that nobody but me will even notice them anyway.
The lifeline suggestion is an excellent one and can save you a lot of frogging.