TrendMiner uses a caching mechanism (referred to as indexing) to allow a fast, interactive visualization and analysis of your time-series data. More info on indexing can be found here: https://userguide.trendminer.com/en/indexing-explained.html
The amount of points which can be exported from the chart is limited by the index resolution (in your case 60s).
To be able to export more data points the index resolution can be increased but this will require a rebuild of the complete TrendMiner index and will therefor also impact other users. A change of the index resolution can only be done by TrendMiner admins. We would recommend to contact your admin to discuss this topic in more detail.