How do I handle this situation?

[LetsRock]

I don't think you need to have the 300BB BR to play a session at a higher limit. I'll usually allocate 100-300SB for a single session if I'm going to stick my toe in the deeper end. That's usually enough to cover a few tough hands in a session. If I'm not on the upswing within that amount, then I'm in the wrong game or it's not my day.

The 300BB thought is targeted as a long term BR, meaning you need that much to cover deviation over several sessions.

There's nothing wrong with taking a shot at a higher limit if you feel you're ready for it. Just remember that if you have a tough session, it'll take much longer to build your BR up to where it was when you return to you comfort zone, than it did to lose it at the higher limits.

A 300BB losing streak is severe but very possible even for the best. Losing that much in a single session seems hard to imiagine.