Genetic Mapping! Two-factor cross!?

I agree with your answer. This is how I did it:

First multiply all rfs x100 to get map units and make numbers easier to work with. We have all crosses with a1 so we can use this to anchor the map.

a3 and a6 are very close together. We know a3 is closer to a1 than a6 - so the first 3 we have mapped are a1, a3 and a6.

We can now use a3 to map a7 and a11.  a7 is further from a1 than a3 is, so it comes after a3 and is also further from a3 than a6 is. On the other hand a11 is closer to a1 than a3, so it lies between a1 and a3. Now use a7 to map a8. a8 is further from a1 than a7 so comes after a7.

That is the first part of the map made - a1----a11---a3-a6----a7------a8. Not to scale obviously. As a8 is further from a1 than any other locus, we know there are no other loci to the right of a8. We have also used up all the information for a3 a6 a7 and a8 so we can forget about them.

We can now use a11 to map a10. a10 is closer to a1 than a11 is so it is between the two of them. Now use a10 to map a2. a2 is closer to a1 than a10 is so it lies between the two of them.

Now use a2 to map a5. Using the process as above a5 lies between a1 and a2. Use a5 to map a9. a9 is between a1 and a5. Finally use a9 to map a4 and you find that a4 lies between a1 and a9.

You can always check the order of 3 genes by adding the distances. e.g for a1, a4, a9

a1....11..a4...12...a9

........25.................

These are approximately equal so the order is correct.