I just put a gallon and a alf in my car and now when I start it the check engine light comes on and the car shakes. It still runs and drives but when I stop it starts up again. What can I do? I don't have the money to take it to a shop. Can anyone help me?

Some auto parts stores will attach a code reader to the data link connector, located under the dash, for free. One or more codes are likely stored in the ECM, which should tell you the source of the trouble.

Alf probably doesn't like it down there in your tank.
Why were you putting only 1.5 gal in? Maybe you just stirred up bottom sludge or water and it's in your gas line and fuel filter?