Repair it yourself

I have got my new pack with the Squire Fender Stratocaster electric guitar and the 10G amplifier. I found this guitar fantastic for the price I have paid, about 100 euros along with a bag, a strap and the cable. For such a cheap instrument one can expect to find things to improve, like the neck of the guitar which was hard to play with because the height of the frets. So I decided to loose the strings and lower the frets with 600 grits sand paper. Well I started with 600 grits paper sticked to a wooden box to make it flat, but the procedure was too slow, so I changed to 280 grits first. I went over and over the frets to remove material until I thought they would be more comfortable to play. But this is a delicate thing because if frets are too low or not well leveled then your guitar may sound buzzing or out of tune. Once the frets were low enough I leveled them by putting a cutter blade on the first three frets, then moved the blade up and down always touching the middle fret. If I he