never done it before, seems alright, except i was taught the tone was 'AUM' or 'OM' for the third eye chakra, not 'Thoth'.
i will advise you not to focus on one single chakra, open up all the chakras leading up to the third eye. later, yes, you can focus on one chakra more than another if it seems to be blocked more than others, but it's ill advised to just work with one chakra. the third eye chakra seems to be the most common one people want to work with because it has to deal with clairvoyance. if this chakra is shut energy can pool here. people with under active third eye chakras tend to rely on others to make decisions and are confused. over-active is bad as well, you'll day-dream too much and suffer from wicked headaches because, again, the energy is pooling. the energy must flow evenly through all 7 chakra's, one cannot be greater than the other or it upsets the balance.
try the meditation, but just keep in mind you should work with the other chakra points as well.