I think you went and scared yourself silly for no good reason regarding your blood pressure!
A) 135/73 after walking around in a public place is actually not a bad reading at all.
You then got anxious
, so naturally your next reading was higher!
B) You say you went and walked around the second time for about 15 minutes...did you wait and REST for at LEAST 15 minutes before taking your BP again? My guess is that you didn't.
C) Any infection can elevate the blood pressure temporarily.
D) Those public BP monitors in stores can be very inaccurate especially if batteries are low.
E) Not sure what you mean by "irregular" heartbeat/murmur. If you feel a "skip" now and then, this is relatively common and usually totally benign. Just upsetting and/or irritating.
F) If you have true sinusitis, this can cause the dizziness plus you would need antibiotics.
Might as well kill 16 birds with 2 stones and get a full physical to check ears/nose/throat and to get a proper baseline on your heart and the rest of you(!)
My guess is that as an exercising 23-year-old who is also non-smoking, non-drinking, and in general an energetic guy, you'll pass with flying colors!!!