Oscilloscope trace not quite square
Two issues come to mind:


Is the ground clip of your probe connected such that you get the shortest possible connection to the return of your signal source? (If the logic IC or FPGA has supply pins buffered with capacitors, connect your probe's ground clip directly to the ground node at these capacitors.)
Is your probe compensated? It's not enough to use a 1:10 probe for good signal quality, you also need to match the probe's capacitance to the scope input's capacitance. Related: This online tutorial, this answer and this answer.