Hey stacie!
No one can make you do this except you! That being said, here are some things to consider.
1. How did you get to the hot dog and Doritos? Were they already in the house? Then, get those foods out of the house!

Were they somewhere else, like in a store? That is, did you have to go out and buy them? Well, don't go there! Don't buy them! You can pretend you're in a trance if you like, but the fact is, unless someone physically holds you down and shoves food between your clenched teeth, YOU are the one doing the eating.
2. Do you know where the gym is? Yes. Do you have a way to get there? Yes. OK, so

step away from the computer! Get your keys! Put on your clothes and shoes! Drive to the gym NOW!

That's what it takes. It's not hard except for the first shove out the door and into the car. Make a deal with yourself: You only have to stay for 10 minutes. Walk on a treadmill or ride an exercycle, for 10 minutes. This is just to ease you into it.
3. It's NOT going to feel natural right now because it's a CHANGE!

You have to change what you are used to doing. You have to be willing to try to change.
4. Stay aware of what you're doing and what you're thinking. Funny how folks can leap in the car and drive to McD's, but they just can't figure out how to get to the gym. Those darn cars, they have a mind of their own!

You get my point.
Good luck! Keep TRYING!

Jay