Too small?

Do you mean they hit the stone gaurd? you can remove that

If the discs (assuming you got new) fit ok but the caliper doesn't, then you can buy an adaptor from various brake specialists to make them fit proparly.

If thats not the problem, could be the discs are not correct for the integral handbrake. 170 or 190mm IIRC. Maybe worth checking you have the correct parts.

HTH