the day name needs to be converted to a number, you can use a case statement for that something like:
SELECT discipline, `day`, `from`, `to`, activity, venue, CASE `day`
	WHEN 'Monday' THEN 1
	WHEN 'Tuesday' THEN 2
	WHEN 'Wednesday' THEN 3
	WHEN 'Thursday' THEN 4
	WHEN 'Friday' THEN 5
	WHEN 'Saturday' THEN 6
	WHEN 'Sunday' THEN 7
END AS day_nr
FROM sessions
WHERE discipline = 'Trampoline'
ORDER BY day_nr ASC


