I have never had sex but I started to shave my penis for the first time and I noticed a tiny red pimple on the base of my penis I shaved my penis for the first time on saturday (it is now monday) and I discovered a small red pimple like thing at the base

It . It sounds like you are right in your guess about it being a small cut. Keep the area clean and dry. Instead of bactine, if you are not allergic you may want to use neosporin. It will coat the area and act as a barrier since it has a vaseline like consistency. If you can avoid sex until it heals that would be best since any friction will cause the area to possibly open up further. In addition, if you do decide to have sex, please use a condom, open sores or cuts are more susceptible to bacteria and thus infection. Take care.
Here are some... Based on the reported sequence of events, the concerned spot is most likely related with shaving-injury. Dr. Jackson is right; follow her advice. However, the fundamental issue is why you want to shave the area where is hard to shave leading to proneness to cut. So, if possible, do not shave there anymore since shaving there is more a fad than necessity. Best wish... .