Finally it worked out! The number t-shirt is finished, and I'm very happy with the end result! It was not difficult at all, if you know just what to do ;) So I'm gonna tell you right now.
1 Print the number (or anything you want) on the transfer paper. Important: print the number in mirror image!
2 Put the number upside down on the t-shirt and iron on the baking paper for 1 or 2 mintes on the highest level.
3 Wait until the fabric is cooled off and then pull off the paper.
4 Iron for 10 secondes over the baking paper to seal the numbers. That's it!
Now you have a great unique t-shirt. You can print whatever you like on the transfer paper and iron it on your t-shirt! How cool is that? Hope u like it! And good luck if you gonna try!