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