Where you say "While integrating the size of s and t is taken as 45x1 but sometimes it becomes 30x1" , you are apparently referring to the array sizes of s and t which are being sent to your 'fun' integrand function. That is characteristic of many integration routines and the integrand functions must be written so as to properly handle any size array that is sent to them. You can read about this at:
This has nothing to do with the size of your integration result, which is determined by the integrand function along with the two sets of integration limits. If you obtained 10^90, look at your integrand to see why.
If you want more detailed information, you should show us how your 'fun' and the four integration limits are defined.