I was diagnosed with UC in 2009.
I see my GI whenever I have a flare - otherwise every 3-6 months follow-up.
Getting regular blood work ensures you do not have increased WBC and other inflammation markers. Just a prevention from getting a really bad flare and treating it in time.
I get the flu shot because its kinda required component for us at work NOT because of UC.
In addition to these, my GI recommended I get colonoscopies every year.
AndI eat a well-balanced diet.
I stay away from foods that trigger a flare-up. I am a vegetarian and for me spicy foods and milk cause problems.
In short - experiment on foods and see how your gut reacts to it. If it bothers you do not eat it.
Some doctors say eat everything. However, from my personal experience, certain foods during stressful situations trigger flare-ups.
Hope this helps.

I don't get a flu shot. I have if and my GI doc has just declared me in remission. Only took 4+ years to get me there.

I watch what I eat. I eat fruit and vegetables but not very often. I watch the amount of red meat that I eat and eat more white meat.

When in a flare I saw my doctor every month. Now I see him every six months. I get a colonoscopy every year. And because of on of the meds I take I get my blood drawn each month. And liver enzymes checked every other month with a blood test. I get a remicaid infusion every six weeks which has helped put me into remission.

I have had UC since 1987, been through lots of different gastros over the years, but none have said exactly what you describe. Discuss your symptoms with 10 different gastros and I guarantee you will get at least 7 different opinions. Seeing him twice a year is somewhat arbitrary, unless you are fortunate enough to have very predictable flares at the same time every year. If you are not flaring, what does he want to see you for? Regular blood work is very important, but you didn't mention what treatment he prescribed. If you go on any of the standard treatments, your liver enzymes should be monitored. But you can do that by visiting your primary care/family doctor, who can fax the results to your gastro. As for the flu shot, I've never heard that the flu can cause a flare. I have heard of a link between pneumonia and UC flares, and I have experienced it about 5 times over the years (a flare followed by pneumonia a month or so later).
So overall this isn't totally off the wall advice, but there are many other things he could have said. For example: you will need to get regular colonoscopies. : ) Maybe once a year until your symptoms are under control. Also, you will be on medication the rest of your life. And lastly, you will be one of the lucky ones if you can figure out which foods cause you to flare.
Of course, no one wants to hear these things in their first visit to a gastro.
As the years go by, you will probably go to other doctors, especially if someone advises surgery. Dont ever be afraid to seek a second opinion! Its your body, and this is a serious disease. There are almost always other options. About 5 years ago, the gastro I was seeing basically gave up on me because I had so much trouble tolerating the treatments. He referred me to a surgeon. But I never went to him; instead I found another gastro who I had met during a hospital stay, who happened to have call that weekend.
I want to caution you about just trying to tolerate a flare; it is gets out of hand, you will have to see the gastro or you risk a serious health crisis on many levels (chronic dehydration, blood loss, electrolyte imbalance, heart problems, etc etc). Find some sort of treatment you are comfortable with. For several years I took no preventative treatment (Asacol, Imuran, and Remicade were not working or were not an option), so the only thing left was prednisone. I gained about 30 lbs and became a weak, confused, miserable person who could not figure out whether it was the chicken or the egg (the UC or the prednisone). I finally agreed to try Humira and I will NEVER take prednisone again unless it is to save my life. I also take my own version of preventatives in the form of fish oil and vitamin E, and recently I've added turmeric and vitamin K, all for their anti-inflammatory properties.
Take some time to study this disease, and don't be afraid to talk to your doctor. Its going to be with you for a long time, unless you are very lucky, so take it seriously and take care of yourself! My best hope for you is that it was a misdiagnosis and you are soon symptom-free!! Otherwise, look to groups like this for caring people who have been where you are going and are willing to help you through it.