The first time I went to Europe I was 19 and it was part of my university. I was part of a larger group and that helped. I was there for two terms--January through June--and we had a lot of room for travel with classes that met Monday-noon Thursday, ten days off in the middle of each term and three weeks off between terms. This was pre-cell phones. My parents sent me off with a list of European contacts that my parents had from business and family. I also had a letter introducing me and providing contact info for my Dad home and business. Granted it's easier today, but having local people to call on eased my parents' minds.
So, when I first got there, my initial weekend trips were with fellow students and one that was a group skiing adventure in Austria. In the first term, did a solo journey to Strasbourg where I met up with a high school friend's former roommate. I was fun to meet her and see Strasbourg, but I was really glad it was only a week end as it soon became clear that she was into a bit more risky behavior than I was. My big trip was to Greece where I was planning to meet up with friends. Our plans went awry and I ended up traveling alone. I did call on the Greek contact from my parents and that helped. But, I have to say it was a bit scary for a while. I used that experience to travel alone to France, where like you I had some French from HS, but not much. I stayed strictly in hostels where I met people.
I have to say that I was two years older than you when I did this. I had been away to college for a year and a term. I had done a weekend to Chicago and a few other week end trips on my own. Granted I did not have the cell phone advantage.
So, my question to you, is, have you traveled anywhere on your own? Did you plan it yourself? I think that you're a little late to be planning a trip to Europe for this summer. Here's one compromise to consider. Go to the course and then travel for a week or ten days afterwards on your own. By then you'll have confidence in your language. You will probably will have been able to do week end trips to gain experience. If you want to just go to Europe this summer, you need to do more planning. Where are you going? How are you going to travel? Where will you stay? What do you want to see?
I hope others have more suggestions. I want you to travel in Europe by yourself, but I know at 17 I would not have been ready. At 19, I had the best time ever. BTW you should look for what Andy Steves is doing with weekend trips for college students.