T.F.
Ask around in your neighborhood. There are usually lots of high school/college girls around.
Out HOA has a secured website and the people interested in babysitting, pet sitting, etc can post on that site and give details of experience, etc.
Word of mouth is a good way to get a good sitter.
My 17 yr old sits for 4 families regularly in our neighborhood. It all started with just 1 job 3 yrs ago. SHe has most every weekend booked.
Think about your pay as well. We guaranteed $40 for the night and then paid on top of that which ended up being $60-$80 per week for our date night.
Now that daughter is babysitting, she averages $12-$15 per hour cash in my area. That said, she is not one to sit on the couch with her phone... she is very engaged with the children... arts/crafts, mani/pedi, gingerbread houses, etc.
Good luck! Coppell is a nice area and I am sure there are some great sitters in your neighborhood!