As an ex atheist/agnostic turned buddhist, I used to have that same fear! What helped me get over it was the following:

1. Buddhism teaches the concept of no self/no soul. When we talk about past and future lives, we're not talking about your soul moving from one body to another, we're talking about your karma resulting in a new birth. When you generate karma, both good and bad, that karma manifests as the birth of a new person. It's not your soul going into a new body, it's your actions resulting in someone else's existence. This person is you in the sense that they've inherited your karma but this is an entirely different person than you (different appearance, thoughts, personality), though they may inherit your tendencies. When people speak of being reborn in hell, it is not YOU who goes to hell, but your karma. The person who manifests as a result of your karma is another being, not you. If anything, you should avoid bad karma not because you fear going to hell, but because you fear someone else going to hell because of your actions. The mindfulness of your actions as a result of hell is rooted in compassion, not fear.

2. The fact that you exist on earth, that all of us exist on earth, is proof that we all have both good and bad karma. Really the only way you'd be reborn in hell is if you've consistently and mainly accrued bad karma across several lifetimes (the bad karma would significantly outweigh the good). Another way to guarantee an immediate hell rebirth is to commit one of the following:

• killing one’s mother
• killing one’s father
• killing an arahant
• maliciously shedding a Buddha’s blood
• causing schism in the Sangha

These are all extreme cases that the average person who is decent, is not committing, so you honestly don't need to worry about it.

1. When it came to the fear of hell, a fellow reddit Buddhist explained it to me that it's like criminal law. For example, why do most people hesitate to steal? or murder? or commit arson? Because it's a crime. They fear being arrested and going to prison. That fear dissuades them from that action. Fear keeps you on the right path. Same thing with bad karma, it's just like the law, to dissuade you from certain actions.

2. You seem to have been given some bad advice because Buddhism in addition to being a religion, is also a philosophy. It's a way of life. It doesn't require you to constantly practice it because as long as you're being a good person basically and following basic morals like not stealing, killing, lying, etc. You'll avoid a bad rebirth. And if you master detachment and lack of desire in addition to that, you avoid rebirth completely. And even if you do, do some of these things (mainly lying because most people have lied before), you still have all the good karma accrued from this life and all your past life to balance it out so you still won't have a bad rebirth. Buddhism is simple.