Can you tell me where I went wrong?

I lost several tournament games in a row recently, all against higher-rated players.

2262333
2262341
2262324
2262348
2262359
2262368
2262366

I felt like previous to this, my confidence in Hex was growing, and even defeated a few stronger players in a previous tournament. But now I think I must be doing something wrong.

My question is - for each game, what was my first obvious mistake, and what was my biggest mistake?

Thanks.

Maybe play the centre of a delta

https://littlegolem.net/jsp/game/game.jsp?gid=2262333&nmove=4
Both corners you played suboptimal, the furthest move on the diagonal is usually(!) the optimal

https://littlegolem.net/jsp/game/game.jsp?gid=2262341&nmove=16
Here the same pattern as above + you then played a ladder that is favourable for white, because he just makes huge line cutting the entire center

https://littlegolem.net/jsp/game/game.jsp?gid=2262324&nmove=5
You have to try to understand the corner fights (joseki). Find purpose in them. In this case you should utilize top-left side of the board, instead you picked f4 which is stronger in center and would be useful to finalize game quickly, but in open board doesn't make sense.

https://littlegolem.net/jsp/game/game.jsp?gid=2262348&nmove=5
Here, apart of c5 being quite suspicious, you had a great chance to give huge problems to black with 6.g8 which basically kills e9 and claims entire center. Later, depending on black move you could continue with top-right (j4) or bottom-right (j11)

I think that's enough homework for you :)

2262333: Play the 5-4 point, not the 5-5 point in the acute corners. Favor obtuse corners when they're available. Learn obtuse corner joseki: http://trmph.com/hex/board#13,j4j2k2j3k3 http://trmph.com/hex/board#13,j4i3k4k3j3j2l3 http://trmph.com/hex/board#13,j4i5
2262341: Play k12 not l12. Move 3, you already have a stone on the south edge, put one on the north edge (such as at j4). Again, you're playing 5-5 in the acute corner, you should play d5.
2262324: a13, not b12.
2262348: Always swap a4. c5 is not a good second move, play the obtuse corner (d10). For move 4, you need something on your east edge, like j4. By the time you play i9 (which should have been i10) it's too late.
2262359: Don't play the center on your first move. Take a corner. d10 would have been good. After black plays j9, attack with one of the typical joseki (http://trmph.com/hex/board#13,j9j10i10 http://trmph.com/hex/board#13,j9g11)
2262368: Move 3, play the obtuse corner (j4) if you want a stone on this edge. Also if your plan was to play the ladder to the left, you should have extended your territory to the right first: (http://www.trmph.com/hex/board#13,a10c3d4c11i9j4g7g8e9e10f9f10g9g10h9i10d11d10h10g12h11h12i11i12j11j12k11k12l11l12)
2262366: Swap a4. Play the 4-3 point (j11) not 4-4 (j20). On move 4, you need to put something on the left edge, you've already got a stone on the right edge.

In case it's not clear, the 5-4 point is a move like j9 for black, or i10 for white