To cut off as many of the incoming 'money for dog walking, who cares' comments as possible: not only did OP take the position because it was an opportunity to further their studies, but not all student assistants get paid money-what the student gets to learn is considered payment.
I don't know much about your situation ( whether this is your first 'proper' job etc) but maybe you can look at this as a sort of 'paying your dues'? Nobody starts at the top, you have to work your way up! Maybe this job will lead to better things or develop into the sort of role you want in time?
You may also get to learn a lot in the periods where you're not out with the dog that will help develop your learning. :-/