I think I managed to land myself in, what I'm assuming is, debt. My inventory tells me that its currently -151.0 gold and I think its increasing each time i go to explore. Is there a way to raise that back up or does it continue increasing?
Or am I better off starting a new game again?
There are weekly costs associated with various stuff around the castle, like maintaining the orcs, the cubi, etc. You may have also been hit with some events that lower the castle funds. The best way to increase income is to capture/trade with villages—see the second link in my signature for details, but the game is currently bugged so that several village capture events don’t add to your actual total, so if you’ve already captured some, that might be the culprit.
As to how to proceed from here, kinda depends on what week you’re on and how many villages you’ve captured. If you’ve only captured two or three and you’re already past week 21, you can probably turn things around by negotiating trade with more villages—savescum for generic capture events (the black screen asking whether you want to conquer the village, trade with it, or leave it alone), those are guaranteed to work.
If it’s before week 21 or you’ve captured 5 or more villages and your income’s still in the red, you’re probably best off starting over; you need 500 gold in the castle to avoid a game over at week 21, and you’re going to have a really hard time getting your income to a reasonable rate if you don’t have many villages left to capture.
How to go further than this to get to rastadal?
You seem to have overshot, it should be to the southwest of your current location. If you go straight west, you’ll run into a road leading south that should take you there.
There’s also some maps linked in my signature, if those would help.