Congrats on the new bike and high hopes for the new life! You got a great bike to work with too. 4 days is not really enough time for your backside to get used to riding so I'd give it a while longer before buying a new seat but bike shorts are a must. I usually use liners to wear under other shorts because nobody needs to see me in spandex and they make a huge difference. If after a month or so with the shorts you still feel the seat needs replacing then have at it. I say wait because at this point they're all going to feel bad. Make sure your seat is adjusted properly for you, pop into the bike shop that did your tune up and ask them to critique your setup. Best of luck!