I'm not sure what you mean by "safe", but it's okay to be a beginner! Jams are for people to have fun together. Worst that can happen is, you don't finish your game in time, but it happens to everyone. Don't worry about it.
Viewing post in Participate to an game jam
Jams are to create games based on certain rules and themes.
Some require you to work in a group, others do not. You can make a game completely by yourself, you can create your group or you can join another group.
The truth is, there is everything, it is only a matter of searching.
I advise you to be honest, for example, if you join a group saying that you know how to draw pixelart, and then you are not able to do it, then yes, someone might get angry. But it will be because you are not capable of fulfilling what you promised.
If you're honest and say you're learning, nobody's going to get mad.