Is there an option to delete the incomplete multipart uploads after X days?.

Yes. While this functionality has not been exposed in the control panel yet, the Spaces API supports using lifecycle rules to delete incomplete multipart uploads. For example, using AWS cli, you can configure a rule like so:

$ aws s3api --endpoint-url=https://bucket-name.nyc3.digitaloceanspaces.com \
    put-bucket-lifecycle-configuration \
    --bucket example-space \
    --lifecycle-configuration \
    file://lifecycle.json

 Where the contents of lifecycle.json look like:

{
    "Rules": [
        {
            "ID": "Remove uncompleted uploads",
            "Status": "Enabled",
            "Prefix": "",
            "AbortIncompleteMultipartUpload": {
                "DaysAfterInitiation": 1
            }
        }
    ]
}