Full sized spare replacing donut spare

I just bought a 98 Saturn for my daughter. The car came without a spare tire so I picked up a full sized used spare from a local junk yard (185/60R15 on car w. 185/65R15 tires). However it doesn’t fit in the well made for the donut spare tire. My question is what is the best way to secure the spare in the trunk?

Lots of duct tape?

There really is no good way to secure it. And it uses up a lot of trunk space which is limited in any case. My suggestion is that you admit your mistake and get her a normal donut spare like everyone else.

I secure my full sized spare with a strong bungee cord and a rope made for climing. Here is a diagram.