Option 1 - you could try leaving it until tomorrow evening in the hopes that your period might have lightened by then. You could then just continue alternate days (but on odd nights - ie. day 5, then 7, instead of day 4, 6, 8 etc.). I don't think that minor adjustments like this make a huge difference to how it works, overall.
Option 2 - just take it orally tonight. One night shouldn't have a major impact on how it makes you feel, unless of course, you simply can't take it orally for other reasons.
Option 3 - do you use tampons? If so and if you would really rather try to insert it tonight - you could try popping the uterogestan capsule into your vagina just before inserting a tampon and gently push it upwards with the tampon. That way it should stay in place high up and hopefully get absorbed. Good luck!