These "little" preludes and fugues are not to be sniffed at ! They're pretty difficult actually. As you say the prelude is not bad, apart from a few small slips, but you are rather groping your way through the fugue. Sounds like you were just being not familiar enough with it yet. Not a reason to stop ! Only a reason to practise a bit more
One advice I'd give is to play less legato. This applies to the prelude mainly here. Always leave some air between the notes, especially in the closing bars. That does doesn't sound good legato.
Registration changes would IMO not be appropriate here. I don't find them necessary in most Bach. Except for pieces that have repeats or are clearly laid out in different sections (e.g. O Lamm Gottes unschuldig from the Leipziger Chorale).