All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
First of all, we ask Allah to reward you for your keenness on wearing the hijaab, and we ask Allah to bless you with guidance, piety, chastity, and richness and preserve your religion for you.
Lying is forbidden, and a Muslim must avoid it except for a necessity, such as the case when lying is the only means to achieve a lawful purpose; in which case, it would become permissible.
Lying means saying something that is not true. So if you were not really busy at that time, then you have lied and you must repent, unless you said that statement as a Tawriyah, in which case there is no harm on you. Tawriyah is saying something which has more than one meaning and intending a meaning different from what the listener is likely to understand. It is better to use Tawriyah than to resort to lying, as we have previously highlighted in fatwa 88412.
Finally, you should know that you are not required to wear the hijaab in the presence of your uncle, whether he is a direct uncle or an indirect uncle [such as the uncle of your father or mother].
Allah knows best.