Preparing for a competition, after 36 years

Hello, As brief intro as possible, I'm 54, was a university swimmer in 1980s, quitted swimming completely since, got back to the pool last October (2018) for cardio exercise to lose weight, so have swum slowly a few miles a week and lost weight well. The weight is satisfactory and stable now. Two weeks ago, my brother told me that our senior nationals is being held in a few weeks. Senior swimming is not popular in my country, so there are enough lanes left for me to join without having to quality. I've tried training in the past two weeks, and found that I still can swim in fast mode. My times (push from wall) are now in the top-three of both events that I'll enter, based on last year's result. They are not even good for USMS standard, and the top guys here are really fast, but I guess I can hold my own in the second row. I've found that so many things have evolved. When I was young, I never wore goggles and cap, and there was no jammers, and I had no knowledge of streamlining and underwater dolphin kick. Well, senior athletes in my country don't talk much, not to mention that there are only a few of them and no forum for it. So I decided to join this forum for some suggestion you may have for a returning newbie. I've improved my times a bit in the past two weeks, now what to do for one week to go (I'll swim 100 and 200 free)? I read online that nowadays swimmers shave down? Would that really help? I'm quite hairy but never shave any body part except my face. Any suggestion for mental preparation is also welcome. I'm helplessly getting excited. Thanks in advance.