For Part I
Running is a pretty common way to express anxiety in a dream.
The fact that you are running on all fours could mean that this anxiety is related to something very basic and instinctive. (There have been a number of recent posts here related to running on all fours in dreams - it seems to be common.)
Standing in a long grass also has a primitive feel to it. (I'm thinking of the African savannah).
The fact that your anxiety is related to being near your old school also makes me think that this anxiety is related to something in your past. It could have to do with something that happened to you in your past that is affecting the way that you feel about a situation that is going on in your life today.
The tripod-type structure that is blocking the school could be a physical representation of the protective mechanism that is blocking these painful thoughts from your conscious mind (maybe not blocking the memories completely, but stopping you from feeling the full weight of all the emotional pain).
The gymnasium in the dream could represent energy and strength. Maybe a message that you have the energy and strength to deal with whatever problems you are facing.
It's interested that you are relieved that you didn't stop to see any familiar people. That also seems like an indication you are trying to avoid something from your post or something about yourself that you find uncomfortable.
Here is some information on
dreams about school that might interest you.
The sea is a common dream symbol of the unconscious and the emotions, while a highway can represent a path in life.
Part II
A
city in a dream very often represents your hopes for the future.
In waking life, a city is just a piece of land until people try to make it into something better by building homes, shops, adding transporation, etc.
It is often the same in a dream. A city is what you/your life could be if you used your talents and skills to make your life better.
I think finding the beautiful city near the sea is a message that if you can get in touch with what is going on in your unconscious and with your emotions , and if you recognize and use your strengths, you can make your life what you want it to be.
I think the boy child represents a part of you that is strong and knows what you should do. I'm guessing from your name that you are female. If so, since the boy is your own age, I think he could represent the "masculine" part of you - the part of you that is strong, assertive and determined.
The fact that you and he go on the ferry together - something that you would never do (I'm guessing because of fear) - further indicates that he is the part of you that makes you strong.
When you start to feel uncomfortable being with boy and wish you were with the boy you do love instead (a real boy in waking life), it makes me think that you are having trouble with reconciling being in a relationship with someone else and developing your own strength and independence.
At the end of the dream you give up and let your father hold you too tightly. It sounds like on the one hand, you want to have more control over your own life, but that you don't know how to gain control. It's interesting that at that time you are pining for the boy you love. It does seem like you are trying to learn how to balance independence with being in a relationship.
It would be helpful if you described a little bit about what your relationship with your father with like. Was he very controlling or was he easy-going? Did you rely on him for advice and guidance?