Maybe you have already solved it, but if it happens again check Windows > Settings/Preferences > Preferences > Interface

The lowest option is Mouse scroll wheel enable/disable

Bye

Dave

Another tip: before mirroring the model, be sure to align all the vertex which lie on the mirror plane, so you won't have holes and overlapping faces after the mirroring.
To do so, a quick way is...

Hello, can u help me with this issue?
How can you close a planar hole in a NURBS surface?
For example, you create a curve, and u extrude, or loft it into a surface. Now you have 2 holes, one at...