Did I do something wrong?

No.

On my next trip, will my Schengen tourist visa be cancelled or will they refuse me entry?

We can't predict the future. There's nothing in your question to suggest that outcome is likely.

Am I on the radar with German authorities now?

Yes (I surmise), you made more than a handful of short trips, including some to a country which arguably has a slightly more relaxed approach to personal use of recreational drugs.

One year I made a number of short business trips to Rotterdam which I was asked about and was held up a little while my bags were searched before being allowed to proceed. I was not told why. On subsequent trips, nothing unusual happened.

Of course, since they didn't ask you about anything, there is no way to tell why they chose to handle you differently on that occasion.

Did I do something wrong?

No.

On my next trip, will my Schengen tourist visa be cancelled or will they refuse me entry?

We can't predict the future. There's nothing in your question to suggest that outcome is likely.

Am I on the radar with German authorities now?

Yes (I surmise), you made more than a handful of short trips and your pattern of past travel, dress, luggage, appearance, state of mind etc did not, in some minor way, fit the usual patterns they see from the greater majority of travellers.

One year I made a number of short business trips to Rotterdam which I was asked about and was held up a little while my bags were searched before being allowed to proceed. I was not told why. On subsequent trips, nothing unusual happened.

Of course, since they didn't ask you about anything specific, there is no way to tell why they chose to handle you differently on that occasion.

Did I do something wrong?

No.

On my next trip, will my Schengen tourist visa be cancelled or will they refuse me entry?

We can't predict the future. There's nothing in your question to suggest that outcome is likely.

Am I on the radar with German authorities now?

Yes (I surmise), you made more than a handful of short trips, including some to a country which arguably has a slightly more relaxed approach to personal use of recreational drugs.

One year I made a number of short business trips to Rotterdam which I was asked about and was held up a little while my bags were searched before being allowed to proceed. I was not told why. On subsequent trips, nothing unusual happened.

Did I do something wrong?

No.

On my next trip, will my Schengen tourist visa be cancelled or will they refuse me entry?

We can't predict the future. There's nothing in your question to suggest that outcome is likely.

Am I on the radar with German authorities now?

Yes (I surmise), you made more than a handful of short trips, including some to a country which arguably has a slightly more relaxed approach to personal use of recreational drugs.

One year I made a number of short business trips to Rotterdam which I was asked about and was held up a little while my bags were searched before being allowed to proceed. I was not told why. On subsequent trips, nothing unusual happened.

Of course, since they didn't ask you about anything, there is no way to tell why they chose to handle you differently on that occasion.