Will it be hard to teach myself piano?

I actually took private lessons with a wonderful teacher from when i was 5 years old til i was about 9 or 10. Unfortunately, by now (13 now..only a month or so to be 14) i have forgotten much of what i have learned :/. I can read notes, but it takes me a few seconds to find those keys on my piano. Therefore, when i try playing some of my favorite pieces of music, i have to play it very slowly. Also, i find it hard playing my left and right hand together...my friend recommended i practice my left hand til i have it nearly memorized, then do the same for my right hand and slowly put them together. I had given up piano before, but now i have a great urge to start again so that I can play some beautiful music for family and friends. Right now I have the sheet music for "Pan's Labyrinth Lullaby" or "Mercede's Lullaby". This is such a beautiful piece, and I was told it wasn't very hard, but it's challenging enough for me. So, any tips or words of advice would be very much appreciated :D thank you.