SPOT THE MISTAKE: Not long time after I started at this school I made lots of new friends.
NOT LONG AFTER I started at this school I made lots of new friends.
SPOT THE MISTAKE: It wasn’t until I have been studying English for about three years that I began to feel comfortable speaking it.
It wasn’t until I HAD been studying English for about three years that I began to feel comfortable speaking it.
SPOT THE MISTAKE: I watched a little bit of televisión before of leaving the house this morning.
I watched a little bit of televisión BEFORE LEAVING the house this morning.