The advantage of a small gas torch is that disassembly becomes much easier.
Remember anything that can be soldered can be unsoldered.
If it doesn't look right, or isn't on square take it off, clean it up and redo.
Doesn't take long.
Learning to tack solder first can save a lot of simple errors.
Also in future always build the chassis first to ensure good runnning. This is not to make life more difficult, but sometimes adjustments are required concerning wheel/motor clearances and it is much easier to do when unassembled.(Don't ask how I know).
A final note, there are lots of postings on this website by talented builders with copious photographs.
Just do a search for Sandy, Jazz, N15 etc. Worth any number of text books.