DIY function generator with an operational amplifier
I suppose you are talking about the following distortions:

The visible slope in the rectangular waveform
the plateau in the triangular waveforms (this is a result of 1.)

As you provide no voltage scale to you plots, it is hard to say if the slew rate of the 741 is the problem.
Options:

You can remove C3 from the circuit. That way you will force U3 to use its maximum
slewrate.
If that is not enough use another Opamp with a larger slewrate.