Sounds like your anxiety is more intense this time because of the length of this particular trip is something new for you, and that you will travel solo. Is this your first solo trip? Your pre-departure nerves seem to already have you checking and re-checking your trip details and plans - which is fine. You may even find yourself slightly OCD during the trip checking to make sure you have your passport, credit cards, ATM card, etc.
Everyone gets a little anxious at some point. I once spent so much time planning the first part of a year long round the world solo trip and was so busy with that and packing for it that it wasn't until I was halfway over the Pacific Ocean that I had this fleeting "Wow…what did I just do?" moment - it passed before the plane touched down in Australia.
What you need to accept is that not every minute of every day will go smoothly. This is even more true if you are one of those Type A compulsive planners who has every waking hour planned out for the entire 7 weeks. Accept that some things will go wrong - planes, trains and buses will be delayed or possibly missed, you may end up in a part of a town where finding someone who speaks English is difficult, you will get lost at some point and will need to ask for directions, you might get some bad service from someone - get over it. As long as you aren't bleeding or dead, you'll be able to work through it. And don't over plan. Some of my best experiences that year where things that just simply happened off the cuff - no planning at all.
You're anxiously thinking you are going to be alone the entire 7 weeks - you aren't. You think no one in their 30s travels solo except for you - wrong, they do. Those traveling solo actually have a far easier time meeting and interacting with other travelers and locals. You're actually seen as more "approachable" by others when you aren't huddled in a group, or joined at the hip with another traveler partner like a significant other or a best friend when you are typically tuning everyone else out because you have each other to talk to. I've had many other travelers and locals approach me to strike up a discussion in all kinds of places - grocery, outdoor market, pubs, restaurants, over coffee, bookstores, on trains and buses, in hostel kitchens/lounges, at the laundromat, museums, concerts, sitting on a bench in a park - you name it. If you want to have interactions with people while you are traveling, then I heartily suggest you go against the impulse (and advice) to stick your nose in a book, map or stare at your iPhone whenever you aren't sightseeing. That's a sure-fire way to send a signal to others that you want to be left alone.
Be open to talking and possibly hanging out with people who are not in your immediate age group for a drink, coffee, meal or sightseeing. I was in my 30s yet had plenty of times where I had a drinks with people 10-15 years younger than me, and I did some hiking or had dinner with some people who were 20-30 years older than me. You're going on a RS tour and although I've never personally been on one, I've seen their tour video and the demographic certainly skews more towards the 50-75yos. Consider signing up as a member on Couchsurfing International's website - you don't have to stay at another member's place - many members are simply interested in meeting up with visitors to their particular cities and just having a coffee or meal or showing them around for a few hours.
Overall, just relax and enjoy.