Assuming that the use of the word "template" in the question is not just a red herring, then the answer should be one that refers to working on the project without one.
Without a template, in the sense of not having any indication of how something should be done, improvise (as already answered) is perfectly reasonable.
However, the more common sense of template is:
(1) a gauge, pattern, or mold (such as a thin plate or board) used as a guide to the form of a piece being made : (2) a molecule (as of DNA) that serves as a pattern for the generation of another macromolecule (such as messenger RNA)
something that establishes or serves as a pattern
In that sense, working without a template can mean a couple of things.
done without mechanical aids or devices · freehand drawing
by hand and not by machine : by manual methods · We have to enter the data manually.
So, with this interpretation, we have something else:
- There weren't any available templates for my project so I had to finish it (freehand / manually / by hand).
Based on the example sentence, this interpretation seems less likely than does the one that makes use of improvise.
However, the use of template seems odd to me. Because if there is really a lack of "project guidance", I would more naturally assume that it's not a template that's missing, but a blueprint, schematic, or set of instructions. (Ikea furniture does not come with templates but with assembly instructions.)