Belize to Guatemala, heading due south?

[JGBYJ]

I'm going to try to cross from El Ceibo(approximately lateral from Palenque)
It's a recently open crossing that someone suggested I try out as he wants to take a 4x4 group through, apparently all dirt and questionable road(should be fun, and since most people going a similar way go through Frontera Corrazal it will be a bit different) but I may be able to make it all the way to Belize. If I do that, I would prefer to head south again, is there any way to cross from southern Belize into Guatemala and be closer to Honduras that way?

My whole route has pretty much been winging it, I had a paper map that covered USA-Honduras but I didn't look at any planned routes and just kinda followed the gulf around, I don't want to dead end and then back track in southern Belize if I can avoid it.