I am going to record a new songs and to be well prepared I changed my strings, the way I stretch them is to set them and wind them two step higher than normal E strings to sol#note A ti do# and etc... and keep this position for 24 hours by rewinding them again and again whenever I could, did I damaged them, I checked the 12 fret and discoverd that they do not excactly match the free string tune, should I change the strings before recording, my guitar is COMPAS classic and the strings are DADARIO EJ45. I have not checked the 12 fret before on this guitar, Thank you very much.
By just leaving the strings tighter than they should be for a day or two isn't going to bed them in. The main problem point is where they wrap around the post on the machine head. Also the bridge, where the strings are tied on a classical guitar. At those points, the strings are pulling against themselves. The better way is to get each up to pitch, then pull along the length. I don't pull like a bow, but rather stretch out a hand and push with thumb, pull with ring finger, along the length of each string. This needs doing (on all guitars) several times, until the tuning of each string settles. Often, the next day, they still need a little strtch before tuning stability is attained.
To make life easier, you only need two or three wraps around the posts, making sure the string isn't over itself. Although, the unwrapped strings can sometimes be stopped from slipping by doing just that. And, not so obvious, wrap it the right way- left or right!
The 12th fret issue is probably one that pre-existed, unless you've used different gauge strings. It's the intonation of the guitar, and on a classical, often can't easily be remedied, as the bridge is fixed.There are loads of Q&A on this site referring to this problem, but with a classical guitar it's best left to a luthier.