I have data that looks like this:
1000 13 75.2
1000 21 79.21
1000 29 80.02
5000 29 87.9
5000 37 88.54
5000 45 88.56
10000 29 90.11
100
You really can't display 3 columns of data as a 'surface'. Only having one column of 'Z' data will give you a line in 3 dimensional space, not a surface (Or in the case of your data, 3 separate lines). For Excel to be able to work with this data, it needs to be formatted as shown below:
13 21 29 37 45
1000 75.2
1000 79.21
1000 80.02
5000 87.9
5000 88.54
5000 88.56
10000 90.11
10000 90.79
10000 90.87
Then, to get an actual surface, you would need to fill in all the missing cells with the appropriate Z-values. If you don't have those, then you are better off showing this as 3 separate 2D lines, because there isn't enough data for a surface.
The best 3D representation that Excel will give you of the above data is pretty confusing:
Representing this limited dataset as 2D data might be a better choice:
As a note for future reference, these types of questions usually do a little better on superuser.com.